The aim of this paper is to elucidate the role of hydrated silicate monomer on the hydration of alite. A combination of XRD Rietveld method and ²⁹Si NMR analysis was used for quantifying hydrated silicate monomer. The thickness of hydrated silicate monomer layer was the same as the thickness of silicate gel layer in hydrated alite, which was calculated from the depth-direction distribution of hydrogen atom that was determined by nuclear resonance reaction analysis, which was performed by Livingston. The discussion based on the thermodynamic phase equilibrium theory indicated that the hydrated silicate monomer was existed in the form of ion in the solution. This implies that the silicate gel consisted of the calcium leached layer including the hydrated silicate monomer. In addition, it showed that the divergence point from the basic curve in relation to the produced amount of hydrated silicate monomer and the hydration reaction degree was consistent with the starting point of the accelerated period in hydration of alite with the addition of CaCl₂ as accelerator. These result obtained in this study could support the metastable barrier hypothesis that was proposed to explain the mechanism of induction period and acceleration period during alite：the metastable CSH produces the hydrated initial stage, and this plays as selective membrane that permeate calcium ion but not silicate ion. As proceeded the hydration of alite, the ionic concentration in liquid phase was changed, the equilibrium was shifted from metastable C-S-H to stable CSH, resulting in transport of silicate ion toward the out of alite particles. This is the trigger of starting the accelerated period of alite.

View full abstract

The cement industry emits large amount of CO₂. Blended cement is effective in CO₂ reduction because 60％ of the CO₂ is emitted by burning limestone. But blended cement has the problems which are decrease of early age strength and resistance to neutralization. It is thought that the problems are resolved by increasing alite（C₃S）and free lime（f.CaO）. f.CaO and blended material has influence on hydration and fluidity. This paper discusses the influence of f.CaO and blended material on the early age hydration and fluidity of blended cement.
In case of cement without blended material, the increase of f.CaO caused decrease of fluidity. Ca（OH）₂ was generated by hydration of f.CaO. The Ca（OH）₂ increased the specific surface area and decreased the amount of superplasticizer adsorbing on a unit area. It was thought that the decrease of fluidity caused by decreased the amount of adsorbed superplasticizer. The fluidity was improved by blending fly ash（FA）or blast furnace slag（BFS）. In case of the cement that includes much f.CaO, FA was more effective than BFS. It was considered that the improvement was caused by dilution effect of blended material which decreased hydration product. There was an upper limit of f.CaO. In this research, the limit was 2％.

View full abstract

It is expected that the amount of fly ash（FA）emitted from coal fired power plant is increased. It is important to utilize effectively FA as blended material. But FA blended cement has the problems which are decrease of early age strength and resistance to neutralization. It is thought that the problems are resolved by using the cement including more alite（C₃S）and free lime（f.CaO）than those of ordinary Portland cement（N）. This paper discusses the hydration reaction of blended high-alite cement containing FA or blast furnace slag（BFS）as blended material.
The blended cement replaced with FA or BFS by 20％ showed as great heat liberation as N. And the porosity of 3 or 7days cured blended cement were lower than N or same. It is expected that the early age strength of the blended cements are comparable to that of N. The amount of Ca（OH）₂（CH）in the hydrated blended cements were close to that of N. And the amount of CH was increased by increase of f.CaO. It is expected that the resistance to neutralization is improved by increasing the amount of C₃S and f.CaO in the base cement. Increase of f.CaO accelerated early hydration of BFS and tended to accelerate hydration of FA.

View full abstract

High content belite clinker with a phosphorus oxide（P₂O₅）content up to 1 percent was test produced and subjected to research of its effect on the properties of clinker and cement. With an increase in P₂O₅ content in clinker, content of alite decreased and that of belite increased. The change amount of alite and belite was the same as N clinker studied previously and calculated value. We assumed that all P₂O₅ was a solid solution in belite as C₃P. Thus, it was suggested that belite is doped with P₂O₅. P₂O₅ effect on the cement color and setting time was little. With an increase in P₂O₅ content in clinker, the compressive strength and the hydration heat until age of 28 days were decreased. The change amount of compressive strength and hydration heat were corresponded. This study or the result of this study could contribute to quality control high content belite cement.

View full abstract

The model of C₃A-Gypsum hydration model is modified for considering existence of solid-solution of monosulfate and C-A-H in AFm phase, formation of C-A-H on the C₃A particle surface, and diffuse double layer of C-A-H. In the hydration reaction, the phase equilibrium and the surface complexation reactions were assumed to be used in the model. For W/S＝2.0, the hydration reaction proceeded by the phase of equilibrium. During early age of hydration for W/S＝0.6, phase equilibrium and surface complexation caused the hydration process. At later age of hydration, not only the reaction between Ettringite and unhydrate but also Ettringite and C-A-H continuously occurred producing the AFm phase.

View full abstract

Calcium silicate hydrate（C-S-H）is a dominant hydration product of cementitious materials, hence its chemical composition and physical properties also affect the properties of concrete. In particular, the formation of microstructure and diffusion of ion were influenced by the specific surface area of C-S-H. Therefore, to accurately evaluate the performance of concrete, it is important to clarify the specific surface area of C-S-H, which is a dominant hydration product of cementitious materials. Moreover, in the case of use of mineral admixture such as blast furnace slag and fly ash, it is known that Si in C-S-H was substituted for Al. However, physical properties of Al substituted C-S-H have not been clarified.
The purpose of this study is to estimate the relationship between chemical composition（Ca/Si ratio and Al/Si ratio）and specific surface area of C-S-H. The relationship between the composition and specific surface area of C-S-H will also be investigated using synthesized C-S-H, C-A-S-H（Al incorporated C-S-H）and that generated from various cementitious materials. Experimental results show that the amount of adsorbed water and specific surface area of synthesized C-S-H and C-A-S-H are affected by its Ca/Si ratio and Al/Si ratio. The low Ca/Si ratio C-S-H is greatly affected by the effect of Al incorporation for specific surface area. The specific surface area of C-S-H generated from blast furnace slag and fly ash is greater than that from Ordinary Portland Cement. The result of various cement paste show same tendency as that of synthesized C-S-H and C-A-S-H.

View full abstract

For prediction of physical adsorption of chlorides, the surface complexation model is usually used；chloride ions adsorb on the SiOH sites on the surface of C-S-H. However, Pointeau et. al suggested that there were two types of SiOH sites：silanol and silandiol sites. Silanol sites are present in the pairing tetrahedron position of silicate chain, while silandiol sites are in the bridging tetrahedron position. Both sites generated surface charge by the deprotonation and ionization. Most of past studies considered only one type of SiOHsite, and could not reproduct the chloride adsorption isotherms. This implies that when considered only one site, one cannot predict exactly the physical adsorption of chloride ion. In this study, we consider two different SiOH sites for chloride adsorption and enhance prediction model of physical adsorption of chloride ions. ²⁹Si and ²⁷Al MAS-NMR studies indicated that the density of pairing and bridging tetrahedron position in C-S-H may change at the Ca/Si ratio and the substitution of Al atom for Si atom in bridging position. Thus, the effect of Ca/Si and Al substitution on surface potential was examined and then the density of silanol and silandiolsites was quantified. Next the thermodynamic equilibrium constant of surface complexation was calculated using zeta potential data in NaOHand Ca（OH）₂ solutions and chlorides adsorption. It can be confirmed that our refined model can predict more exactly the physical adsorption of chloride ions on C-S-H as compared with previous model.

View full abstract

Cementitious materials is planned to be adopted for constructional member of the intermediate storage facility for low-level radioactive soil and debris spans. It is reported that Cs contained in debris is adsorbed to cementitious materials. It is important to understand the phenomenon because adsorption of Cs to cementitious materials may affect the designing of the facility.
In order to ascertain the adsorption mechanism of Cs to cementitious materials containing mineral admixtures such as Fly Ash, ²⁹Si, ²⁷Al and ¹³³Cs MAS NMR spectra obtained from synthesized Calcium-Aluminosilicate-Hydrate（C-A-S-H）. The ²⁷Al MAS NMR spectrum of Cs adsorbed C-A-S-H shows structural change；The intensity of signal at about 70ppm, which attribute to Al₃^＋ indicating coordination number 4 and substituting for bridging Si in SiO₄ chain, increased by Cs adsorption. That Al substitution an imbalance of electric charges around Al because the charge of Al（＋3） is one less than that of Si（＋4）. To resolve this imbalance Cs（＋1） is attracted to Al. This phenomena is considered one of the main mechanisms of Cs adsorption for C-A-S-H.
The ¹³³Cs MAS NMR spectra of Cs adsorbed C-A-S-H is different depending on Ca/Si ratio. The ¹³³Cs NMR spectra of low Ca/Si ratio C-A-S-H consists of at least two signals. It may suggest that there are two mode of adsorption of Cs in C-A-S-H.

View full abstract

We have established the analysis method of ultra small-angle X-ray scattering（USAXS）to interpret wide X-ray scattering profiles of calcium-silicate-hydrate（C-S-H）combined from ultra small-angle scattering profiles in a synchrotron radiation and wide angle scattering profiles in a laboratory. By using this method, we have investigated the C-S-H structure before tobermorite（5CaO・6SiO₂・5H₂O）crystallization under the hydrothermal condition and the effects of γ-Al₂O₃ and gypsum addition on the crystallization. The C-S-H with γ-Al₂O₃ addition consisted of platy or disk-like particles mainly. On the other hand the C-S-H with gypsum addition consisted of fiber- or rod-like particles. By using the disk-model or the rod-model as the form factor and the mass fractal model as the structure factor, we could fit the calculated profiles to the measured scattering profiles of both systems. In all samples, a clear correlation between an equivalent spherical radius（Re）calculated from the model fitting and an average chain length of Si-tetrahedron in the C-S-H structure on ²⁹Si solid state NMR analysis were observed. Consequently, micro and macro structure of C-S-H affected subsequent crystallization of tobermorite. The tobermorite formation mechanisms in these systems were also discussed.

View full abstract

The slag concrete which blast furnace slag is activated by Na₂CO₃ to reduce CO₂ emissions has been studied. In this study, chemical compositions of hydration products in this slag paste were analyzed by the SEM-EDX method. As the results, Hydration products of slag paste were hydrotalcite, AFm phases and C-S-H. Hydrotalcite was lower Mg/Al ratio than theoretical value and formed in the inner product domain of slag grain. Chemical composition of C-S-H in the slag paste was vastly different from that in blast furnace slag cement type B（JIS A 5211, BB）paste. Ca/Si ratio of C-S-H in the slag paste was 1.1, which is much lower than that in BB paste, and large amount of Al and Na was incorporated in C-S-H. These values are consistent with that of previous papers. Na was thought to be incorporated in C-S-H because the Na/Ca ratio was increase with an increase in Si/Ca ratio.

View full abstract

Slag-blended cement has chemical disadvantages needed to be overcome when used in various materials. Some of the disadvantages are due to difficulty in precisely understanding the hydration degree of BFS in slag-blended cement. Assessment of the hydration degree could provide deep understanding of properties of slag-blended cement. This study investigates the method which was suggested by Sagawa et al., to measure hydration degree of Blast-furnace slag（BFS）in slag-blended cement. They invented the method by combining crystallization by heat treatment and quantitative XRD-Reitveld method. According to their study, unreacted BFS can be crystallized by heat treatment, and determined quantitatively by XRD-Rietveld analysis using external standard method. However, because the method still needs more validation before it is routinely used, it should be compared to a different method. In this study, spiking method was used. Spiking method is also known as standard addition method, in which different amount of unreacted BFS is added in each division of slag-blended cement sample. From the results in this study, hydration degree of slag determined by spiking method was found to be similar to the one by the previous method. Therefore, the method established by Sagawa et al., has been proven to be useful to determine hydration degree of BFS.

View full abstract

We investigated the clinker formation process using the high-temperature X-ray diffraction of a combination of high-speed semiconductor and the high-temperature heat attachment. As a result, the formation state of the high temperature phase of the clinker minerals which have hitherto only been identified in a single phase, we were able to observe in-situ by heating the cement raw materials. Reaction of the formation and disappearance of each clinker minerals in high temperatures, were consistent with previous findings. Formation temperature of the high-temperature phase of each clinker minerals were similar to previous findings. Effect of coexistence clinker mineral and clinker material composition for the phase transition temperature of high-temperature phase is small.

View full abstract

This paper describes the adsorption behaviour of polycarboxylate-based dispersant（PC）on the cationic site of alpha-alumina（aluminum oxide）fine particles when added calcium ions. Five PCs consisted of graft copolymer with different side chain/main chain ratio was used to make clear the impact of chemical structure of polymer on the adsorption of PC. PC adsorption was measured using a set of solvents containing different amounts of Ca（NO₃）₂. PC adsorption results indicated the site of PC adsorption increases when the addition of Ca（NO₃）₂ increases. A surface complexation model was also used to estimate the amount and kind of adsorption site. Analytical results show that in the presence of calcium ions, the cationic surface site in alpha-alumina consists mainly of >AlOCa^＋, which is driven from binding of a calcium ion to >AlO^－ on alpha-alumina. The obtained correlations between the density of cationic site >AlOCa^＋ and the adsorption of PC can indicate that at saturated adsorption of PC, the number of cationic site per the surface area of alumina in which a molecule of adsorbed PC is occupied reduced with decreasing the number of cationic site on alpha-alumina. This implies that PCs do not absorb uniformly but absorbed locally on a surface of alpha-alumina surface. Furthermore, it could be found that the number of carboxyl group on main chain of PC contributed PC adsorption, which was estimated from experimental PC adsorption data and the number of cationic surface site estimated by surface complexation model, was decreased as increasing the number of cationic site despite the kind of PC. This suggests that PC presents the multi-layer adsorption.

View full abstract

Understanding the transport of chloride ions into concrete is of primary importance for designing the durability performance of reinforced concrete structure. In order to predict the chloride ion diffusion, integrated thermodynamic model has been developed taking into account of surface complexation reactions. On the other hand, the chloride transport is influenced by the micro-pore structure such as porosity and tortuosity. The actual path for chloride transport in cement paste is very complicated or tortuous in particular in nanoscale. Furthermore, the transport of chloride ion is also affected by the electrical properties of pore wall. It implies that the effect of tortuosity of pore includes the effect of electrical properties of pore wall. In this study it is assumed that the size of effective pore is 5nm or less, in which scale the effect of electrical properties of pore wall is dominant. The tortuosity of cement pastes with different porosity and diameters was estimated by fitting the value estimated by integrated the thermodynamic model to experimental values. The results showed that the tortuosity of pore increase from 1.0 to 2.5 with increasing of the porosity of less than 5nm pore. The increase porosity less than 5nm pore enhances the path length of very narrow and continuous pore, so that the effect of electrical properties of pore wall is dominant. This can explain the correlation between the tortuosity and porosity of less than 5nm pore.

View full abstract

Immobilization of chloride ion is important for applying to the building into the salt damage environment like seaside. It is known that the aluminate phase（C₃A）produce AFm phase such as Friedel’s salt or Kuzel’s salt which immobilize chloride ion into its layer structure. In hydration, the ferrite phase（C₄AF）generate less heat compared with C₃A, so it is strong point to prevent thermal crack. Since C₄AF also produce AFm phase, it is expected that C₄AF hydrates can immobilize chloride ion. The authors have been reported the immobilization of many harmful anion such as iodide ion and chromate ion in hydrated products of C₄AF. This paper describes the hydration products in C₄AF-CaSO₄・2H₂O-CaCl₂ system and the immobilization of chloride ion in hydrated products of C₄AF.
In this system containing CaCl₂, Kuzel’s salt or Friedel’s salt was produced. Therefore, it is clear that the immobilization of chloride ion is occurred. Fe-containing gel was also found in every hydrated samples. The main elements of Fe-containing gel are Ca and Fe. Although Cl is detected from Fe-containing gel, it seems that Fe-containing gel immobilize less chloride ion than AFm phase since the density of chloride ion is smaller than that of Friedel’s salt.

View full abstract

Nowadays, the sulfate attack on concrete structures is one of the serious problems in the Middle East region. On the other hand, rate of C₃A and C₄AF in cement clinker has increased, related with the increase of amount of industrial-by-product. Therefore, the purpose of this research is to evaluate the sulfate resistance of specimens mixed with C₄AF and gypsum after autoclave curing. The influence of C₄AF and gypsum on the formation mechanisms of tobermorite also have been examined by X-ray diffraction analysis and FT-IR. As the result of sulfate immersion test, the results of length change ratios of specimens with autoclave curing were much better than specimens with water curing. At low additional ratio of C₄AF, tobermorite peak was detected by X-ray diffraction analysis. On the other hand, tobermorite peak was not detected at high additional of C₄AF, and the frequency of 980cm^-1 and 1,050cm^-1 was confirmed by FT-IR. Therefore, improvement of sulfate resistance for the specimens with autoclave curing is due to the generation of tobermorite at low additional ratios of C₄AF and the generations of Si structures like tobermorite at high additional ratios. Also, the formation of tobermorite was increased by the addition of gypsum, and the generation of hydroxyl-ellestadite that is intermediate during autoclave curing of tobermorite was suggested at specimens mixed with gypsum.

View full abstract

In previous studies, the mechanism of shrinkage reducing agent（SRA）attributes the reduction of the surface tension of gas-liquid interface of pore solution in cement paste and the water content at the same relative humidity decreased due to this reduction of surface tension, consequently, the reduction of water content leads the reduction of shrinkage of hcp in the context of the capillary tension theory. In this study, the length change and mass change of cement paste containing different SRA concentration under different relative humidity. The obtained results showed that shrinkage of hcp is reduced under the lower relative humidity range in which capillary condensation has not been confimed and there exist SRA concentration dependency. Accordingly, the mechanism of SRA is not due only decrease in the surface tension of pore solution, but also the hidden mechanism which acts in the lower humidity range.

View full abstract

Cement industry is one of the energy-intensive industries. Though Japanese cement industry has achieved top-class energy efficiency in the world, the development of the further energy saving technology is needed from the view point of global environmental protection such as the reduction of carbon dioxide and fossil fuel consumption. We reported low burning-temperature type clinker by adjusting of mineral composition previously. In this study, we carried out burning test of the low burning-temperature type clinker by actual kiln. As a result, the low burning-temperature type clinker was able to be burned in actual kiln, because the free lime was decreased less than 1％. Furthermore, it was estimated that the low burning-temperature type clinker was able to be sintered at 1,300 to 1,350℃, which was approximately 100 degrees less than the OPC clinker on the same condition. And the heat consumption rate was able to be reduced around 5％ compared with the OPC clinker. Next, we evaluated the cement manufactured by actual finish mill. As a result, we confirmed that the properties of the cement and the concrete were at the same level as OPC.

View full abstract

We developed an energy-saving cement for the purpose of decrease in the production energy of Ordinary Portland Cement（NC）. In the previous study（1）we found the possibility to reduce the production energy and to maintain the quality of cement, by increasing in the C₃A content in clinker by 4％ and increasing in the admixtures content in cement by 5％. In this study we conducted production tests using small-scale plants which imitated commercial plants, and evaluated the production energy, property, and durability of the energy-saving cement. As the result we found that the production energy of the cement was decreased by 8.5％ compared to that of existing NC. The property and the durability of the energy-saving cement was equivalent to those of existing NC, except sulfate resistance. Moreover we conducted a construction test of concrete using the energy-saving cement, and we confirmed the test construction was finished as well as the construction using existing NC.

View full abstract

This paper examined the effect that the particle size of the materials gave in physical properties of the mortar. We performed the experiments to operate the particle size of the materials by using Powder-Aggregate Material PAM：crushed and screened aggregate. The following conclusions were made. 1st：the flow value of the specimens mixed fine PAM was lower than the plane specimen. A positive correlation was accepted between the filling rate and the flow value. 2nd：the compressive strength of the specimens mixed PAM was higher than the plane specimen. A negative correlation was accepted between the filling rate and the compressive strength. This result suggests that the pore structure becomes subdivided as the filling rate decreases. 3rd：it was not able to confirm the change of the static modulus of elasticity by mixing PAM. This result suggests that the particle size of the materials does not affect the modulus of static elasticity. 4th：the drying shrinkage of the specimens contained the materials finer than 75μm sieve increased. 5th：the carbonation progressed deeply as the particle size of PAM became small. A negative correlation was accepted between the filling rate and the carbonation depth. This result suggests that the permeability increases as the pore structure becomes subdivided.

View full abstract

Spatial structure of air voids in concrete is crucial for not only frost resistance but also strength and permeability of concretes. In this study, spatial distribution of air voids were quantitatively evaluated by applying the point process theory to cement pastes and mortars. Air voids distribution in mortars were simulated by thinning operation for basic point processes. For the sake of easy handling of images, cement paste and mortar images were acquired by flatbed scanner. Then all the air voids visible in images were converted to points. As expected, air voids in cement paste specimens are distributed randomly regardless of air contents. On the other hand, in mortars, random dispersion of air voids is not observed since aggregate partials interfere in spatial arrangement of air voids. Cement paste matrix in mortar can be regarded as a random field. The clustered distribution of air voids in actual mortars was simulated by the thinning operation for a random point process. The simulated patterns have the same spatial characteristics as real distribution in mortars. Furthermore, characteristic distances of air voids in actual mortar are also comparable to those of the simulated patterns. Point process statistics and thinning operation for the point process are useful for evaluating and estimating air void systems in mortars.

View full abstract

Quick-hardening cement is used in urgent repair construction or in cold region to be hardened within a few hours and show high strength at early age. The types of quick-hardening cement are divided into 2 roughly. One is Portland cement with quick-hardening additive, and another is special cement. We have studied about the basic properties of the mortars whose cement was based on quick-hardening cement as ordinary Portland cement（OPC）with amorphous calcium aluminate or calcium sulfo-aluminate cement（SAC）. In the results, we have found the following properties；1）Mortar flow and workable time were influenced by retarder much. 2）Compressive strength at early age was higher when the cement composition was based on OPC with quick-hardening additive. We consider that it was due to the high hydration activity of amorphous calcium aluminate. Compressive strength after 1 day was higher when the cement composition was based on SAC. We consider that it was due to the much amount of quick-hardening constituent of SAC. 3）Expansion strain showed only when the cement composition was based on OPC with quick-hardening additive. We consider that the topochemical formation reaction of ettringite contributed to expansion. 4）Neutralization was showed only when the cement composition was based on SAC. We consider that the lower pH of pore water of SAC based mortar caused to degradation of ettringite by carbon dioxide. And more, we consider that degradation of ettringite may cause specimens porous and carbon dioxide intrudes easily.

View full abstract

Numerous recurrent situations following mixing and pumping of cement-based mortars and concretes cause degradation of fluidity and hardening characteristics. Which, in turn, leads to adverse effects on the quality of workmanship and structural defects. Nonetheless relatively little research on the mixing and pumping energies used for the onsite transport and preparation of mortars and concretes has been directed at the core reasons or mechanisms for changes in technological properties.This work describes and explains the effects of mixing parameters on the mortar characteristics such as hydration kinetics, compressive strength and dimensional stability. The performed investigations indicate that excessive mixing energies lead to accelerated and increased hydration rate, increased early compressive strength and autogenous shrinkage. Hydration acceleration occurred even in the case of fully dispersed mortars although became less pronounced in the case that mixing water was supersaturated with calcium hydroxide.
From these findings, a novel and original idea as to the explanation of underlying mechanisms is presented as follows：the increased dissolution from the active surface area due to the destruction of the passivating initial hydrates layer of cement grains and of the electrical layer（concentration gradient of Ca^2＋ ion）, as well as a transition from flocculation to dispersion. The creation of new cement surfaces leads to the densification of microstructure and to subsequent earlier compressive strength development and increase in the autogenous shrinkage.

View full abstract

Influence of using cement clinker as a fine aggregate on the properties of mortar was discussed. In the results, compressive strength of mortar increased with the increasing replacement ratio of cement clinker to fine aggregate. Moreover, when the fine aggregate was replaced with cement clinker, the effective diffusion coefficient of chloride ions decreased. However, the relationship between the decrease ratio of the effective diffusion coefficient and the replacement ratio of the cement clinker was not clear. In addition, it was considered that the cement clinker that was below 0.15mm acted as a binder. Therefore, a densely packed cement paste layer was produced from cement clinker of this grain size. On the other hand, it was considered that cement clinker that was over 0.15mm acted as a reactive fine aggregate. Therefore, this grain size of cement clinker formed a densely packed interfacial transition zone.

View full abstract

Blast furnace cement paste having a high temperature history due to hydration heat shows the time dependent change of the thermal expansion coefficient and temperature strain remained in the shrinkage side after returning to ambient temperature. This shrinkage caused by temporal change of thermal expansion coefficient could increase the risk of thermal cracking. In this study, the experimental study using a plurality of shrinkage reducing agent was performed for suggesting the method of suppressing the increase of the thermal expansion coefficient due to self-drying. As a result, suppressing effect for the increase of the thermal expansion coefficient have been confirmed and it depends on the type of shrinkage reducing agents, but in case of receiving the temperature history of the maximum temperature 60℃, the thermal cracking risk might been decreased because the thermal strain and autogenous shrinkage are reduced regardless of the type of shrinkage reducing agents.

View full abstract

It is important to evaluate the physical properties of the cement-based materials from pore structure for predicting the durability of cement based materials. Mercury Intrusion Porosimetry（MIP）is widely used for pore structure measurement method. However, it was reported that micro structure of hardened cement paste was destroyed by the drying treatment and applied high pressure. To solve them, low-temperature differential scanning calorimetry（LT-DSC）based on thermoporometry was proposed. However, studies about LT-DSC are few. Therefore, the effectiveness of LT-DSC measurement in pore structure measurement is not clear. In this study, we investigated whether pore structure measured by LT-DSC can evaluate physical properties of hardened cement paste. By comparing the results of LT-DSC and MIP, it was suggested that the measurement by MIP might cause the destruction in micro structure by drying and applied high pressure. It was cleared that it is possible to evaluate physical properties by total pore volume measured by LT-DSC. Moreover, it was indicated that threshold pore radius of the chloride ion diffusion was 7nm by using pore size distribution measured by LT-DSC.

View full abstract

As pressure grows for moves toward a low carbon society, an important issue is how to reduce CO₂ emissions from the cement manufacturing process. To meet the demands of society, CO₂ output is being reduced around the world by adding admixtures to Portland cement. At the same time, the properties of the Portland cement and the amount of admixtures and their quality are unknown to the end user, so problems arise in ensuring stable concrete quality at the construction site. The authors have designed a conduction calorimeter that can help resolve these issues by allowing continuous measurement of hydration heat, which is the heat released when cement reacts with water. Measurement of hydration heat using a conduction calorimeter is a simple method of investigating cement reactions, and it is widely used. However, knowledge of hydration heat output from blended cement systems over the long term is poor and there is a need for it to be studied. In this study, fly ash, limestone powder and blast furnace slag powder are added to the base Portland cement to produce the blended cement. Heat of hydration, compressive strength and total porosity are measured. From the relationship between heat of hydration and compressive strength, a method of estimating compressive strength from hydration heat output is investigated.

View full abstract

A high-pressure triaxial test is conducted on cement paste to understand the mechanism of mechanical performance of concrete under high confining pressure. The obtained deviatoric stress-mean strain relationship demonstrated that the cement paste is independent of confining pressure during ductile deformation with confining pressure greater than 30MPa. The ion-milled surface of the sample inside is observed with SEM, and the obtained contrast of the reflected electron image become darker after the test. This darker contrast is considered to be due to the deformation of hydrates at an atomic level such as crystal plasticity. Furthermore, the pore volume of the sample tested with 400MPa was drastically reduced compared with that of an intact sample.

View full abstract

Hardened cement paste with various inorganic electrolytes was prepared for investigating the effect of pore structure and pore solution on electric conductivity and transport properties. As a result, it was shown that the correlation between the total pore volume measured by mercury intrusion method and the apparent diffusivity of the chloride ion of hardened cement paste was low. On the other hand, it was shown that relationship between the diffusivity of the chloride ion and electric conductivity of the hardened cement paste by the AC impedance method was linear as reported Nernst-Einstein equation. From this result, it was shown that it is possible to estimate the diffusivity of hardened cement paste by the electric conductivity measurement even if pore structure and pore solution of hardened cement paste changed.

View full abstract

The influence of the curing temperature on the compressive strength and the maximum expansion of the cementitious material based on the OPC-AC-CS system were examined. The influence of the curing temperature was differed from OPC/AC ratio. In the case of OPC/AC ratio 3.00, the compressive strength decreased with decreasing curing temperature. On the other hand, the compressive strength was highest at 5℃ in the case of OPC/AC ratio 0.33 and 1.00. If curing temperature was same, the compressive strength was related with the porosity in spite of OPC/AC ratio. However, the dependence of the compressive strength to the porosity was differed from the curing temperature. From the analysis of the phase composition which calculated from the reaction ratio of main mineral, the reason of the tendency was guessed that the difference of the kind and amount of hydrate. On the other hand, the maximum expansion was increased with increasing OPC/AC ratio and decreasing curing temperature. From SEM observation, small ettringite was formed in the expanded samples. In addition, there were tendency that the amount of C-S-H gel which calculated from the reaction ratio of C₃S was a lot compare with non-expanded condition. Therefore, it was guessed that the maximum expansion was increased because ettringite was formed in the dense matrix.

View full abstract

Low heat Portland cement is generally applied to mass concrete construction to make thermal crack of concrete unlikely. While it is known that low heat Portland cement has less resistance against chloride ion attack, the way to add chloride ions immobilized material and expansive additive to low heat cement has been considered to improve. This paper describes the evaluation of salt resistance of low heat Portland cement using with chloride ions immobilized material and expansive additive.
As a result, Ettringite, Monosulfate and Hydrocalumite were generated as hydrates by adding Chloride ions immobilized material（CaO・2Al₂O₃）and Expansive additive in low heat Portland cement. And the amount of hydration products was different as a function of SO₃/Al₂O₃ molar ratio. In case the cement paste with CaO・2Al₂O₃ and expansive additive immersed in 10％ NaCl solution, pore of hardening body decreased, and the chloride ion permeation depth decreased as well. This was considered to be caused by the chemical reaction that immobilized a chloride ion and the physical reaction that decrease quantity of pore by generation of the Friedel’s salt. And it was confirmed that the resistance of neutralization and salt attack of low heat cement using with CaO・2Al₂O₃ and expansive additive were smaller than in case of using ordinary Portland cement.

View full abstract

The growth of waste and recycled materials in Japan is one of the largest challenges nowadays. It has many economic and environmental benefits for our society. This paper investigates the development of high performance concrete, based on the formation of ettringite, using waste and recycled materials. For this purpose, wants to replace the fine aggregate of part with waste and recycled materials. Cement mixed with ground granulated blast-furnace slag, fly ash, gypsum wastes in varying proportions to obtain the optimal production for ettringite based on their chemical response. Compressive and flexure strength tests are performed on the different admixtures to measure the compressive and flexure strength. Measurement for length change of mortar tests are performed on the different admixtures to measure the length change and drying shrinkage. Scan electron microscope（SEM）are conducted on the samples to explore the formation and intensity of ettringite. The test results show that the admixture of using waste and recycled materials has a significant effect on the strength, length change and drying shrinkage improvement of mortar.

View full abstract

The relationship between the air volume obtained through the linear-traverse method and the amount of water absorption or drying was verified for the inkbottle pore volume and the continuative pore volume obtained through the step-by-step MIP method. As for the relationship between inkbottle pores obtained through the MIP method and air voids, the possibility of evaluate the information on air voids volume and size calculated through the liner-traverse method was examined using hardened mortar. A high correlation was confirmed between the volume of inkbottle pores and the volume of air voids. As for continuative pores obtained through the MIP method, their relationship of water absorption and drying in mortar samples was verified. In the water absorption phenomena, a rapid water absorption until about 1 hour after the start of soak and the continuation of slight water absorption until 24 hours after that could be observed. In the drying phenomenon, moreover, the rapid drying proceeds up to 1 hour after the start of the test, and then the relatively larger amount of drying was confirmed up to 3 hours, and a slight amount of drying was measured from 3 hours until 24 hours. For continuative pores obtained through the MIP method, a strong correlation could be found with the amount of water absorption in 1 hour for the water absorption phenomenon and the amount of drying in 3 hours for the drying phenomenon.

View full abstract

This research examine permeable concrete under conditions of gap water saturation in cold areas, and investigate the effects of saturated and unsaturated states on thermal conductivity. This research revealed that thermal conductivity in permeable concrete is nearly the same as in normal concrete, and a linear relation is between void ratio for thermal conductivity. Furthermore, duration of the melting point by influence of the latent heat was confirmed by the temperature measured successively between low temperature and ordinary temperature, and a linear relation is between void ratio for duration of the melting point.

View full abstract

The purpose of this study is to investigate the effect of percentage of total voids and water-cement ratio on the compressive behavior of porous concrete. The relationship between the compressive strength, static modulus of elasticity and dynamic modulus of elasticity of porous concretes is discussed. The porous concretes using cement mortar as binder are prepared with the percentage of target voids of 10, 15, 20, 25 and 30％, water-cement ratios of 22.5, 25.0 and 30.0％. The porous concrete specimens are cured under 20℃ moist for 24h, 70℃ hot water for 1d and 20℃ water for 1h, and subjected to the compression and dynamic modulus of elasticity tests. As a result, regardless of the water-cement ratio, the compressive strength, static modulus of elasticity and dynamic modulus of elasticity of the porous concretes decrease with increasing percentage of total voids. There is a reliable correlation between the compressive strength, dynamic modulus of elasticity and static modulus of elasticity of the porous concretes regardless of water-cement ratio and percentage of target voids. The dynamic modulus of elasticity of the porous concretes is 20％ larger than the static modulus of elasticity of ones. The static modulus of elasticity and dynamic modulus of elasticity of the porous concretes can be estimated by the compressive strength in the same way as ordinary concrete.

View full abstract

It has been the problem to control maintenance, and construct civil structures for long-term. It is considered that concrete after long-term exposure decrease performance by changing properties of cement hydrates, however, there are few studies on analyzing the concrete after long-term exposure. In this study, chemical analysis of the cement hydrates in concrete long-term exposure was conducted. And it is difficult to analyze for concrete by aggregate influence, thus a method of aggregate separation that separate aggregate and cement paste was established in order to eliminate the effect of the aggregate in performing chemical analysis for concrete. The method made chemical analysis in concrete sufficiently accurate.
Therefore, using the method, chemical analysis of the railway bridge concrete built in 1923, and long-term exposure was conducted. It is considered that cement in the railway bridge concrete have low C₃S and high C₂S composition, because the railway bridge built in 1923. From the experimental results, the small amount of calcium hydroxide was produced in the railway bridge concrete. In constrast, calcium carbonate was produced especially in the surface. Hence, not calcium hydroxide but rather C-S-H was carbonated mainly. And in the surface, by carbonation and solar insolation and others, calcium carbonate and dehydrated condensation amorphous silica was produced, therefore specific surface area in paste impaired.

View full abstract

Chloride ions adhering to concrete surface make salt attack. It is possible to remove the ions by high-pressure washing or wash-away by rain and to suppress salt attack. This study’s objective is to clarify primary factors which influence effects of high-pressure washing or wash-away by rain. The parameters considered in this study are denseness of concrete surface, crack width and adhesive properties of chloride. It is, however, difficult to estimate quantitatively the amount of transfer of chloride by simulating real water flow and rain under many kinds of parameters. Therefore, this study proposes a simpler and quicker method than the previous method by using small specimens. The transfer resistance of chloride adhering to concrete surface to water flow is examined by this method. Results of this study are as follows. The higher denseness and wider crack width result in the more transfer of chloride. The amount of transfer of chloride adhering to concrete surface by salt water increases from 2 to 4 times greater than under by deliquescence. The transfer methods are divided into “physical transfer by colliding water（without melting）” and “outflow and penetration after melting”. Most of transfer of chloride has finished in 2 minutes from start and the factor is “physical transfer by colliding water”. The factor “outflow and penetration after melting” hardly happens.

View full abstract

In this study, the authors proposed an evaluation method of concrete pumpability using vibration acceleration as a technique that allows easy direct check of the concrete pumping condition at the construction site. This method indicates that it is possible to evaluate concrete pumpability based on past experiment results. However, studies on various piping routes and how to evaluate measurement results are insufficient.
In this study, concrete was pumped at an actual construction site under four kinds of special piping routes, measurement was made with vibration acceleration and the evaluation method was reviewed based on the measurement results.
The results confirmed that the measurements of acceleration are completely different depending on the piping routes and the measurement position in each condition. The threshold amount of pumpability evaluation using measured acceleration values is also determined.

View full abstract

Currently, lightweight concrete is reevaluated again in the field of civil engineering, and the use of concrete composed with lightweight aggregates and expansive additive for reinforced concrete decks is one of the application of that. The RC deck constructed with the lightweight concrete means that the deck was made by concrete composed with both coarse and fine lightweight aggregates, and added 30kg/m³ expansive additive in order to provide chemical prestress.（Conventionally the use of the additive 20kg/m³）The deck weight is around 20％ lighter than typical concrete decks due to the use of lightweight aggregates, and the unit weight is less than 20.0kN/m³. The fatigue resistance is almost same as conventional concrete decks confirmed by the wheel load driving tests. Subsequently, in order to make sure of the pumpability and casting of the lightweight concrete for road decks, pumpability exam was carried out.
In general, pumpability of lightweight concrete is worse than one of conventional concrete. Before lightweight concrete casting, adequate consideration and pumpability tests are required. This paper described that pumpability of lightweight concrete mixed with Double shaft pugmill mixer is better than the one mixed with Consecutive spiral feather mixer. Furthermore mix efficiency between cement particles and mixing water is variable depending on type of mixers because lightweight aggregate is lighter than conventional aggregate. Thus it is inferred that the presence of cement cluster without water inside is cause of pumpability reduction.

View full abstract

In this study, for the purpose of reliability improvement in quality control, the authors discuss the application procedure of nondestructive tests for quality verification of casted concrete. Recently in Japan, Torrent air permeability test have been increasingly used not only in research field but also in practical construction sites. However, the test method has a problem that the evaluation of absolute quality of concrete based on result of the test is not easy because of the influence of moisture content of concrete on measurement results of the test. From the discussion in this paper, it is concluded that the measurement results suggesting that physical property determined by Torrent air permeability test is just the volume of open pore in concrete, which increases with moisture evaporation from concrete surface. In addition, based on the experimental fact, the authors propose an indicator for quality evaluation with combination of nondestructive-measured values：surface air permeability kT and electric resistivity ρ （or surface moisture content m）.

View full abstract

The connection effectiveness of cast iron coupler connecting device for vertically connected slab members was examined through the results of mechanical behaviors from both the static loading test and low cycle fatigue loading test of jointed full scale precast RC slabs. Main parameters were diameter of anchor rebar and anchor methods of anchor rebar in bottom slab at a connected corner. An anchored anchor rebar with anchor plate method with both D25 series and D38 series could be supported higher static load than one of the monolithic members. Bending anchor D25 series rebar methods at upper parts of main rebars could not be supported higher load than one of monolithic members in spite of a good case in bending anchor D38 series rebar methods. The anchored method with both D25 series and D38 series showed also good hysteresis curves in low cycle fatigue loading with high toughness index. Maximum bending crack widths of connected members were generally larger than ones of monolithic members. An open width at a connected surface was consisted of main parts of maximum bending crack width. Yield phenomena of anchor rebar were also observed at the connected surface in all anchor method befor the failure of the connected slab members.

View full abstract

The purpose of this study is to propose fly ash cement which can be widely used for general concrete structures. Cement samples with alite content of around 70％, by Bogue equation, were manufactured at an actual cement plant. Influences of replacement ratio of fly ash and curing temperature on strength development of concrete using the high alite cement were experimentally investigated. Shrinkage properties and shrinkage cracking resistance of concrete were also investigated. It was proved that strength development of concrete with fly ash cement was significantly improved by using the high alite cement resulting in higher compressive strength at early ages than ordinary Portland cement concrete even at 10℃. It was suggested from the results of restraint stress tests that shrinkage cracking resistance of concrete with fly ash cement using the high alite cement was higher than concrete with ordinary Portland cement.

View full abstract

In this experiment, concrete preparations for precast concrete members in which fly ash and blast furnace slag fine powder are respectively used as the admixture were studied. Their mechanical properties and resistance to the permeability of salt were evaluated by using the design standard strength and curing method as experimental factors. As a result, a large difference was not observed, between the concrete with fly ash or blast furnace slag and the concrete of normal cement alone, in the compressive strengths obtained though standard curing and steam curing. In terms of preparations, when fly ash or blast furnace slag fine powder was used as the admixture, the clear suppression effect for the chloride ion penetration was observed compared with the concrete of normal cement alone. When the soaking period was longer, a more obvious difference was observed in the depth direction.

View full abstract

This paper describes the results of study on strength developments and thermal properties of high-strength and high-flowability concrete using fly ash 120 kg/m³ per unit volume in outer replacement of cement. Fly ash is using with slurry of 65 wt％ in the density. As the result, the main conclusions are as follows.
1）With standard curing, the compressive strength of concrete using fly ash at 7 days ages is the same as that of non fly ash concrete with same water cement ratio. But, the compressive strength of concrete using fly ash at 28 days ages is 5 N/mm² greater than that of non fly ash concrete with same water cement ratio. And, the compressive strength of concrete using fly ash at 91 days ages is 15 N/mm² greater than that of non fly ash concrete with same water cement ratio. This is caused by strength increasing of fly ash concrete due to pozzolanic reaction.
2）₂₈S₉₁ and ₅₆S₉₁ values of compressive strength of concrete using fly ash can be selected small values than that of non fly ash concrete of same compressive strength of core specimens. This is caused by strength increasing of fly ash concrete due to pozzolanic reaction.
3）Fly ash in outer replacement of cement does not give a great influence on temperature rise of concrete.

View full abstract

This paper elucidates experimentally the mechanism of air bubble growing which can cause the reduction of water flow through concrete crack in terms of equilibrium that is the supersaturation of supplying water, which is indicated in geotechnology. Also this paper elucidates experimentally that water flow around air bubbles can cause the acceleration of air molecule’s velocity through gas-liquid interface in terms of the velocity theory by focusing on the growing speed of air bubbles. Furthermore, this paper try to propose the new method of water pass test which is not affected by air bubbles by cancel the supersaturation of supplying water. In that process, there is other mechanisms that the reduction of water flow area causes the reduction of water flow.

View full abstract

Focusing on the self-healing performance of heavyweight concrete used for containment vessels of radioactive substances, studies were made for mixing methods of highly self-healing additives and using heavyweight concrete of required average strength 50 to 70N/mm². The experiment involved the splitting of a rectangular column specimen, followed by wedging a 0.2mm plastic plate between the split specimen to form a simulated crack of the same thickness, immersed in water for a specified number of days, and then evaluated for self-healing performance. The permeability rate from a permeability test was adopted as a quantitative evaluation for the evaluation method, and using microscope for visual observation. As a result of the experiment, it was determined that the mixture having either the expanding material or the fly ash exhibited little self-healing, and it was found that the self-healing was maximized in the mixture having both the expanding material and fly ash.

View full abstract

It is empirically known that using shrinkage reducing agent（SRA）and/or expansive additive（EX）is effective in reducing shrinkage cracks in concrete structures. However, in order to control cracks more rationally, it is necessary that reduction effect of SRA and EX in shrinkage cracks are quantitatively evaluated for design values. In this paper, shrinkage crack characteristics were compared between concrete using SRA or EX solely, or in combination SRA and EX, and plain concrete by investigating crack distribution in uniaxially restrained specimens in which a deformed steel bar embedded. Furthermore, shrinkage crack control effects of SRA and EX were evaluated by determining relationship of drying shrinkage strain measured in the unrestrained specimens with the cracking coefficient calculated from the number of cracks and crack width. As a result, compressive strength and modulus of elasticity of concrete using SRA and EX cured under temperature of 20℃ and relative humidity of 60％ after wet curing at 7 days were equal to or greater than those of plain concrete. The drying shrinkage strain of concrete using SRA or EX was found approximately 10-20％ less than that in plain concrete. SRA and EX were obviously effective in reducing the number of shrinkage cracks and the cracking coefficient. It were also suggested that the crack control effect of SRA could be approximated quantitatively as the decrease in drying shrinkage strain, and that of EX could be as the sum of the decrease in drying shrinkage strain and the amount of expansion-induced strain of about 100-150×10^－6. Further the effect of combined use of SRA and EX could be evaluated as the sum of their individual effects.

View full abstract

To evaluate correlation of Poisson’s ratio of concrete and internal crack caused by drying shrinkage systematically, three different concretes whose parameters are water to cement ratio and shrinkage strain of coarse aggregate were evaluated. Concretes are dried under different relative humidity, i.e. 80, 60, 40, and 20％ RH at 20 degree Celsius until samples attain the equilibrium in mass change and then examined by axial compressive loading. Both lateral and vertical strain of concrete under loading are measured and Young’s modulus and Poisson’s ratio were calculated. As a result, Poisson’s ratio of concrete containing the aggregate with small drying shrinkage strain decreased as the relative humidity of drying condition is low. On the contrary, the Poisson’s ratio of concrete containing the large drying shrinkage aggregate showed no difference under variety of drying conditions. This result represents that the Poisson’s ratio of concrete is a function of internal micro-cracking caused by loading as well as drying.

View full abstract

This paper reports the result of investigation into the effect of void percentage and water-cement ratio on aggregate fretting resistance of porous concrete pavement using ZKT-214：Method of Cantabro test for porous concrete. Test temperature is not specified in the ZKT-214 test method. On the other hand, test temperature in the Cantabro test for asphalt is specified as range in the B010 test method. The test is generally carried out at －20℃ in the case of low temperature. Thus, the effect of different test temperatures were investigated. No significant differences were observed in the Cantabro test for porous concrete pavement at different test temperatures. Aggregate fretting resistance was more affected by void percentage and the mortar-coarse aggregate void ratio（Km）than water-cement ratio. The porous concrete which had smaller void percentage or smaller the mortar-coarse aggregate void ratio（Km）had higher resistance to aggregate fretting. This result was especially related to the compressive strength.

View full abstract

In this study, we investigated experimentally the changes of mass（M）, length（L）, dynamic elastic modulus（E_d）and ultrasonic velocity（V_u）of heated concrete with re-curing duration, and discussed the effects of concrete strength before heating, heating temperatures, cooling methods, re-curing methods on these property changes. It is concluded that a）In case of re-curing in the water, M, L, E_d and V_u increase greatly in the first month, but in case of re-curing in the air they increase very slightly in the first week；b）The higher heating temperature or compressive strength before heated, the smaller the M, E_d, and V_u, but the greater the recovery of there properties in case of water-re-curing. However, length increase of high strength concrete resulting from the water-re-curing is less than normal concrete；c）water-cooling causes greater decrease in the E_d and V_u, but almost doesn’t give obvious effect on the property recovery in the case of air-re-curing, compared to the air cooling.

View full abstract