The chlorides by-pass process has been introduced to many cement plants in recent Japan, because of the increase of chloride content in cement raw materials when municipal wastes are used. The extracted dusts called bypass dusts, containing potassium chloride as the main component were formed in this process. It is necessary to utilize this byproduct; otherwise it will become new industrial waste. This paper discusses the influence of potassium chloride on the hydration of alite, the main component of portland cement, by means of XRD quantitative analysis to determine the phase composition of hydration products. And, the relations between pore structures and compressive strength of hardened pastes with or without potassium chloride has also been investigated. The compressive strength was decreased with the increasing quantity of potassium chloride after the hydration of 7 days. The strength decreased remarkably by the addition of the potassium chloride at 28 days hydration. The dependence of the strength on the porosity of hardened pastes with potassium chloride was larger than without potassium chloride. And the porosity of hardened paste with potassium chloride became larger at the same hydration ratio of alite. Then, the amounts of produced calcium hydroxide were decreased at the same hydration ratio of alite, by the addition of potassium chloride, and Ca/Si ratio of calcium silicate hydrate was increased. It is conceivable that the above mentioned difference of hydration products influences the microstructure and the strength characteristics of the hardened alite paste with or without potassium chloride.
As for the effective utilization of sludge water containing cement and fine particles of aggregate, authors have been studying for several years. Nowadays, JIS A 5308 permits the usage under 3 percent as solids of sludge for the unit content of cement. This study, in order to utilize the larger quantity of sludge water than that now allowed in the mixing plants, is to obtain the basical data on the properties of fresh concrete and of hardened concrete. Especially, the influence of unit content of cement of new concrete and of particle size of aggregate contained in the sludge has been discussed experimentally on the view points of slump, bleeding, compressive strength and drying shrinkage. From the results of this study, it was clarified that a good quality concrete could be obtained regardless of the unit content of cement and particle size of sand in sludge, even though the sludge mass of 9% of cement content and the sludge age of 3 days, provided that setting retarder was used adequately.
The coal-fired power plant shows the increasing tendency from excellent in stability of the raw material supply and the economy, and, therefore, the amount of generation of the coal ash is expected to increase greatly, too. Considering such a current state, JIS A 6201 “Fly ash for use in concrete” was revised in 1999 aiming at the widely use as an admixture for the concrete. The quality of fly ash was classified into four kinds by this revision, and effective use to the field corresponding to each quality became possible. However, the actual results of coarse fly ash newly added (kind IV) are not accumulated enough in this existing state. In this study, to extend the amount of effective use of fly ash, many kinds of concrete using fly ash as a part of fine aggregate or as the admixture for self-compacting concrete were examined.
Authors have been studying for several years on the effective utilization of fly ash, which is a by-product of the combustion of pulverized coal fired thermal power plants. The purpose of this study is to obtain the fundamental data on mixture proportioning of self-compacting concrete incorporating high-volume fly ash, especially how to determine the dosage requirement of superplasiticizer in order to get the self-compacting concrete. The results obtained in this study can be summarized as follows; (1) when fly ash is substituted for not only a part of cementitious materials but also a part of fine aggregate, it can be said that the relative flow area ratio (Γc) is in proportional to the relative funnel speed ratio (Rc). And the gradients of the lines, which means the value of the relative flow area ratio divided by the relative funnel speed ratio, increases continuously with increasing in the percent by volume of portland cement replaced by fly ash. (2) There is a linear relation between the ratio of Γc to Rc and the dosage of superplasiticizer for dosage of powder. Therefore, the dosage of superplasiticizer can be predicted by supposing the aimed slump flow and the aimed efflux time of concrete.
The purpose of this study is to investigate the effects of types of rust-inhibitors on corrosion prevention of reinforcement in aqueous solutions and mortar specimens containing chloride ion. The three types of rust-inhibitors are used. The reinforcements are dipped in aqueous solutions for 28 days and tested for qualitative and morphologic analysis of corrosion products. And the reinforcements in mortars specimens are measured rate of corrosion area after the accelerated corrosion test. The following results are obtained. The corrosion degrees of reinforcements are influenced by the types of rust-inhibitors. The reinforcements are corroded in aqueous solutions without lithium nitrite, as the corrosion products α-FeOOH, β-FeOOH, γ-FeOOH and Fe3O4 are determined by X-ray diffraction and Fourier transform-infrared analysis. As the results of corrosion test in mortar specimens, rate of corrosion area is very small with lithium nitrite, but more or less macro cell corrosion is caused at the boundary between basis part and repair part in all specimens.
60-70% of the concrete lump produced from demolished structures is presently crushed and reused for subbase course of roads, and the rest is discarded. The amount of the demolished concrete is estimated to be 3 to 5 times of the present amount in next decade. The reuse for subbase course will be difficult and recycling of concrete from structure to structure is necessary. In this paper, outline of a technology developed to produce high quality recycled aggregate that satisfy the quality required in JIS A 5005 (crushed stone) and JASS 5 (gravel) is presented. Properties of the concrete using the aggregate were shown to have the same quality as that made by natural aggregates such as gravel and crushed stone.
At present, rapidly decreasing of natural resources and capacities of final disposal sites become serious problems. In the field of construction, it has been said that demolished concrete should be more reused. Most of demolished concrete have been used as base course materials, especially as subbase course materials. However, in view of environmental protection, demolished concrete must be reused as not only subbase course materials but also upper base course materials and aggregates for concrete. The purpose of this study is to investigate whether demolished concrete can apply for upper base course materials that must satisfy stricter standard than subbase course material. Recycled base course materials used in this study were made of massive concrete, which were obtained from demolishing of bridges constructed in 1959. In order to change grading and particle size, crushing method of recycled base course material was changed in several ways. Moreover, to some of them, adjustment of grading with decomposed granite was taken. Particle size analysis, compaction test and California Bearing Ratio (CBR) test were carried out. As the result of tests, modified CBR value of recycled base course material applied initial crushing could not satisfy the requirement for upper base course materials. However, adjustment of grading with decomposed granite and secondary crushing enabled to use it as upper base course materials.
It is well known that alkali-aggregate reaction and chloride attack could cause rapid deterioration and serious damage to concrete structures, initial defects of concrete structures cause a trouble. There happened an accident that the lining-concrete-block of tunnel hit the Shinkansen super express at Fukuoka-tunnel of the Sanyo Shinkansen Line in June 1999. One of their causes was guessed the initial defect, this is called the cold joint. There are few reports on the unity of the concrete with the cold joint. In this paper, the effects of cold joint on bending strength ratio for that of concrete without cold joint was considered experimentally. Production factors of specimens were rodding method, water-cement ratio, casting temperature and construction time from lower layer to upper one. As a result, when even lower layer concrete is not rodded by a tamping rod, the bending strength was decreased. And it was found that bending strength ratio closely was related to bleeding, Proctor penetration resistance needle, mixture proportion and casting temperature. Moreover, bleeding water of lower layer concrete was removed in order to reduce a decrease in bending strength ratio by occurrence of cold joint. As a result, bending strength ratio was improved, in comparison with non-disposal specimen.
The objective of this study was to analyze comprehensively the corrosion cell formation pattern (macro-cell and micro-cell) and the corrosion rate induced by carbonation in concrete with joints or cracks. First, mortar tests were performed using specimens with model defects that simulated cold joints or bending cracks. Herein three important factors that caused steel corrosion were investigated in detail. These factors were: 1) carbonized location, 2) supply of water and oxygen, and 3) water-cement ratio of mortar. Next, concrete tests were performed using specimens with cold joints and bending cracks. The results obtained in this study were as follows; a) 27 cases of which the carbonized location, supply of water and oxygen, and the water-cement ratio of mortar differed were experimented. As results, the corrosion cell formation pattern and the corrosion rate were comprehensively analyzed based on unified conditions. b) In the case of carbonation-induced corrosion with defects, macro-cell corrosion would be formed regardless of the water-cement ratio. Also, the corrosion rate decreased with the decreasing of water-cement ratio. c) The result b) was confirmed not only in mortar tests but also in concrete tests. d) According to above results, it could be said that the low water cement ratio was excellent in the durability for the steel corrosion, when concrete with defects received the influence of carbonation.
It is important to place concrete continuously for construction being joint-less. However, in case placing is discontinued for some reasons, some defects such as cold joints should remain. At the first stage in this study, effects of placing conditions on continuity of concrete were investigated. The flexural and compressive strength at joint between placing layers was almost the same as that of joint less concrete when upper layer concrete was placed over lower layer immediately after the lower layer being revibrated and softened to wet until the initial setting. This result was the same as what is recommended in J.S.C.E. Specification 1974. This principle was deleted from the Specification 1986 onward, because ready mixed concrete had been common and continuously placed by concrete pump. At the next stage, effects of placing time interval on carbonation and corrosion were evaluated by some accelerated tests on specimens compacted without revibration before placing upper layer concrete. This study shows that the longer the placing time interval, the faster the carbonation velocity factor becomes and the earlier the corrosion starts. When the placing time interval is required by some accidents, lower layer concrete should be revibratd in order not to make any defects; otherwise it would be necessary that carbonation velocity and margin of cover concrete depth recommended in the Specification January 2000 should be increased. On the other hand, some type of monitoring specimen would be necessary to maintain the durability of RC structures as there are uncertainties, such as effective use of recycled aggregate, new type of cement such as eco-cement, and change of environment due to industrialization of neighboring countries. It is also clarified that a specimen which is tested in this accelerated test can probably indicate environmental conditions when the specimen is applied to monitor.
In general, MDF (macrodefect-free) cements are produced by using portland cements and water-soluble polymers, and applying mechanochemical processing techniques at very low water-cement ratios, and have flexural strengths of 50 to 70MPa under dry conditions. However, MDF cements have a poor water resistance because of the nature of the water-soluble polymers used, therefore, the precast products made of MDF cements have not been commercialized in the world. MDF cements using a portland cement, a water-soluble polyacrylamide, an epoxy resin and a phenol resin are prepared with various mix proportions by applying a kneader mixing process, hot press molding process and heat cure, and tested for water resistance through a change in flexural strength and water absorption during water immersion. The effects of the mix proportions for the hot press molding process on the water resistance of MDF cements are examined to find out the effective processing techniques for improving their water resistance. As a result, the water resistance of MDF cements is markedly improved by applying the hot press molding process and heat cure to them with the optimum mix proportions, i.e., a polyacrylamide content of 6.0%, an epoxy resin content of 6.0%, a phenol resin content of 2.0% and a water-cement ratio of 8.0%. The application of the hot press molding process to MDF cements is considered to be effective for the simplification of their manufacturing process.
Strengthening technique using CFRP sheet has recently spread widely and strengthening of the existing RC structures deteriorated due to reinforcing steel corrosion is becoming important. Furthermore, it is also important to understand load carrying performance of strengthened RC member during its whole life under corrosive environment. In this study, corrosion of reinforcing steel in RC beams strengthened with CFRP sheet was simulated by the electrolytic corrosion using an external current source. Tension test of corroded reinforcing steel, observation of cracks due to reinforcing steel corrosion in cross section and static flexural test were carried out in order to investigate the influences of reinforcing steel corrosion on load carrying behavior of RC member strengthened with CFRP sheet. Additionally, finite element analysis was carried out using discrete joint elements for the bond between concrete and reinforcing steel, the bond between concrete and CFRP sheet and longitudinal crack due to reinforcing steel corrosion. Reinforcing steel corrosion hardly affected static load carrying behavior of RC member strengthened with CFRP sheet until yield. However, longitudinal distribution of strain in CFRP sheet was changed to be uniform by longitudinal crack due to reinforcing steel corrosion, which was successfully simulated by the finite element analysis.
Flexural and shear behavior of reinforced concrete beams damaged by alkali-silica reaction (ASR) was investigated under monotonous and reversed cyclic loads, mainly focused on the shear resistant mechanism after flexural yielding. In case under the monotonous loads, shear capacity of the beams damaged by ASR was rather increased by the introduced chemical prestress in spite of the strength reduction of concrete due to the existence of expansive cracks. In case under the reversed cyclic loads, the introduced chemical prestress also restrained the reduction of concrete shear capacity successfully within the deformation of 5σy. After that deformation level, however, the effect of chemical prestress almost disappeared and the ultimate deformation tended to become somewhat smaller compared with that of the beams without ASR damage.
The yield stress of the low yield strength steel (LY100) that is used well as a hysteresis dumper is reduced by coarsing grain in the heat treatment process of steel plate production. Therefore, the yield stress rises, when the steel plates are built up by welding to a member. The test specimen that welded 2 sheets of steel plates by butt welding was prepared, in order to investigate the influence of the welding heat input and the cause on the mechanical properties of the steel plate. Gathering the test pieces according to the distance from the weld line, the tension test, chemical composition analysis, optical microscope and micro Vickers hardness test were performed. Also, the change of the yield stress by means of heat treatment become hot after welding was examined. As a result, it is guessed the cause that the heat input record and the cooling under residual stress refine the grain size at the temperature rise part of vicinity of the weld line. And, the grain is coarsened once again by heat treatment for one hour at 850°C after the welding assembly. Therefore it is possible that the yield stress that have rised at the time of the welding assembly is made lower equal to that of the base material.
The FRP adhesion method which uses carbon or aramid fiber sheets for the strengthening of the flexural member of building or bridge has lately become a subject of special interest. The bond strength between the FRP sheets and concrete influences the structural properties of the concrete elements which are strengthened by this method. The strength may be classified into three types according to the direction of force: the shear bond strength, the cleavage bond strength and the tensile bond strength. The authors have reported on the relationship between the shear bond strength and the surface roughness of the concrete. The present study describes the experiments concerning the tensile bond strength and the relations between the bond strength and various surface roughness indexes. The surface roughness of concrete varied by changing the treatment methods, such as, sandpaper polishing, diskgrinding, sandblasting and chipping. Surface roughness indexes, the maximum depth Dmax, the superficial area St, the form factor k, fractal dimension Df and the bearing ratio curve were determined based on the 3D profile measurements of the concrete surfaces. The mechanism for bonding between the FRP sheets and concrete was discussed based on the surface roughness indexes and the observations of the fracture surface of the tested specimens. The conclusions which were obtained from this study are as follows: 1) The superficial area St has the greatest influence on the tensile bond strength among the surface roughness indexes, 2) the chipping treatment reduces the bond strength significantly, and 3) the tensile bond strength increases as the concrete strength increases.
Thin GaAs films were grown on Si (001) substrates by Ga and As beams, consisting of low-energy ions and neutral molecules, without thermal cleaning of substrate surfaces and buffer layers. The energy of the ions in the mixed beams had to be higher than 60eV to grow single-crystalline GaAs films on the Si substrates, In this case, the surface of the Si substrates was amorphized by collisions of ions in the mixed beams. The amorphous Si layer was inserted between Si substrates and GaAs films and served as a buffer layer reliving strain due to the large mismatch and the difference in linear expansion between GaAs films and Si substrates.
The residual stress and strain in GaP layers have been studied using X-ray diffraction and Raman scattering techniques. Samples used in this study were GaP films grown on Si substrates by atmospheric-pressure metalorganic chemical vapor deposition (MOCVD), using trimethylgallium (TMGa) and tertiarybutylphosphine (TBP) as source gases. Lattice constants of the epitaxial layer were obtained from the results of X-ray (004) and (115) diffractions. The lattice constant parallel to the growth surface (a//) was longer than the one perpendicular to it (a⊥). The GaP epilayer was two-dimensionally strained in the growth plane. This is explained by the difference in thermal expansion coefficients. The degree of strain was also verified by the results of Raman scattering measurements.
Evolution of the TRIP strain and the back stress in a maraging TRIP steel (MAVAL X12) is studied experimentally. The stress holding tests under cooling are carried out in order to measure the TRIP performance of the steel in both the axial and shear directions. A linear Greenwood-Johnson relation is observed in the low applied stress range between the maximum value of the TRIP strain and the applied hold stress, being irrelevant to the direction of the applied stress. At the higher applied stress range, the relation becomes non-linear, and depends on the direction of applied stress. When the applied stress is unloaded down to the value of the back stress in the process of transformation, the strain response just after unloading reveals qualitatively that the back stress evolves during transformation from its initial value. The backflow after unloading is due to the Magee effect.
Some creep tests were conducted to clarify the effect of temperature on the drying check of sugi (Cryptomeria japonica D. Don) boxed-heart square timbers during kiln drying. The tensile creep behaviors of tangential direction at the outside layer parts of sugi boxed-heart square timbers and the compression creep behaviors of radial direction at the inner parts of them were investigated. Creep strain and residual strain were larger at 80°C than at 40°C under constant moisture content. Under drying condition, these mechano-sorptive creep strains at 80°C and 40°C were almost same. The creep strains increased approximately like a straight line as the moisture content reduced in the area of moisture content less than 30%. Its gradient can be considered that there is no effect of the temperature. But initial elastic deformation at 80°C was larger than at 40°C. As a result, the relative creep in the high temperature showed lower than in the low temperature. After all, it was supposed that the temperature dependence factor for the restraint of surface check of boxed-heart square timber of sugi was elastic characteristic and was not creep characteristic. The value of creep compliance in compression for the radial direction at the part far from the pith showed relatively low during drying.
Mullite/SiC composite ceramics was sintered and subjected to three-point bending on specimens made according to the appropriate JIS standard. Semi-elliptical surface crack of 100-200μm in diameter was made on each specimen. By using three kind of specimens (smooth, cracked and crack healed), crack-healing behavior and cyclic fatigue strengths were determined systematically at room temperature. And static fatigue strengths was determined systematically at room temperature, 700°C and 1000°C. The main conclusions obtained are following: (a) Mullite/SiC composite ceramics has ability to heal a crack. (b) Crack healed specimen showed higher cyclic and static fatigue strength than as-received specimen, and this fact was caused by crack healing. (c) Crack healed part has enough fatigue strength and most fracture occurred outside the crack-healed zone in crack-healed specimen. (d) Crack-healed specimen has a sufficient strength for cyclic fatigue and static fatigue at room temperature. (e) The static fatigue strength of crack-healed samples at 700°C and 1000°C were similar to the values at room temperature.