An extensive research was undertaken in order to determine the dependence of shrinkage of high and normal strength concrete on the compressive strength and concrete composition. The part of research concerning dependence of autogenous shrinkage on compressive strength is presented in this paper.
Ten groups of concrete, with the total of twenty nine mixtures, were prepared. Concrete mixtures of each individual group were made using the same quantity of water, while the quantity of cement (CEM II/A-S 42,5R) and mineral admixture (silica fume) was varied in each group. Concrete groups differed according to the quantity of water.
Autogenous shrinkage of concrete was monitored together with the influence of initial curing in water on concrete shrinkage. Initial autogenous expansion was noticed during testing autogenous shrinkage, especially on normal strength concrete.
Based on the analysis of experimental results, the dependence of autogenous shrinkage at one day of concrete age on compressive strength was defined. The dependence of autogenous shrinkage at later ages on compressive strength of concrete was also presented.
Finally, the autogenous shrinkage components of best-known theoretical shrinkage prediction models were compared with experimental data.
The ferro-siliceous sacrificial concrete is an important protection material to Nuclear power plant, high density aggregate and high fluidity can lead to occurrence of shrinkage crack. In this paper, the early-age crack and restrained shrinkage crack of sixteen types of sacrificial concrete containing different content of cementitious materials and two kinds of fibers were researched. Results showed that the workability of sacrificial concrete decreased with increasing addition of fiber, and the slump loss resulted from polypropylene (PP) fiber was much higher than that of basalt fiber. The fibers had less influence on the compressive strength, while had greater impact on the flexural strength, which was improved by 10-20%. The reduction of total cementitious materials and replacement ratio increment of mineral admixtures including fly ash and Ground Granulated Blastfurnace Slag (GGBS) in sacrificial concrete could decrease its early-age crack obviously. The utilization of 1.0-1.5kg/m3 PP fiber could extend the cracking time and reduce the crack width of sacrificial concrete and total cracking area. The improving crack resistance capacity of sacrificial concrete resulted by basalt fiber was weaker than PP fiber. The optimized mix proportion of sacrificial concrete mixture was 450kg/m3 total cementitious materials, 50% replacement ration of mineral admixtures and 1.0kg/m3 PP fiber.
It has been reported that owing to a densification of the internal structure of concrete, adding mineral admixtures leads to a more brittle behaviour. Therefore, with the intention of modifying (increasing the strength of) foamed concrete to make it suitable for structural purposes by means of admixtures and lightweight aggregate addition, the effect of these additions on the failure mechanism under compressive and tensile loading using different techniques is evaluated and discussed in this paper. Eight different mixes, made using a pre-formed foam, were investigated with varying density (different foam volumes), nominally 1300, 1600 and 1900 kg/m3, without/with admixtures (silica fume, fly ash and superplasticizer) and lightweight aggregate. The Digital Image Correlation (DIC) technique was adopted to measure the deformations and strains on the surface of a specimen under uniaxial compressive load. Meanwhile, a Video Gauge technique was used to measure the horizontal deformation of discs during a splitting tensile test. From elasticity, fracture and fractal points of view, it was found that, for the same density, brittleness increases with many of the additives while it reduces with inclusion of lightweight aggregate. However, for all mixes, the lower the density (higher added foam volume), the higher the ductility.
This paper discusses a feasible application of wide hoop spacing to reinforced concrete (RC) columns using mechanical splices for longitudinal bars to simplify and accelerate practical construction. Twenty-two RC columns with/without wide hoop spacing at mechanical splices were experimentally investigated in terms of the shear performance. First, a series of experiments on the application of the proposed hoop arrangement to shear-critical columns was conducted. The tests indicated that the negative effects of the proposed hoop arrangement on the column shear performance were limited and that the wide hoop spacing reduced the shear strengths by up to 12%. Therefore, two structural indices for evaluating the shear strength of columns with the proposed hoop arrangement were presented and verified based on the experimental results. Consequently, strong agreement was obtained between the experimental shear strengths and the estimations obtained with the proposed shear strength evaluation method. Then, a second series of experiments was performed to apply the proposed evaluation method to practical shear design for ductile columns. Premature shear failure in the ductile columns was successfully prevented, thus verifying the effectiveness of the shear design. Furthermore, the rotation angles at shear failure after flexural yielding could be appropriately estimated for several columns by combining the proposed evaluation method with idealized bending performance.
This work investigates the role of alumina content in the slag and presence of limestone in composite cement on the hydration and compressive strength evolution of composite cement. A coupled experimental and modeling approach was applied.
Increasing Al2O3 content of slag from 8 % to 12 % has pronounced impact on slag kinetics while further increase from 12 % to 16 % has a limited effect. However, this increase affects the hydrates assemblage across the whole compositional range investigated; the composition of the C-S-H phase and hydrotalcite is modified. Additionally the AFm and AFt phases content changes. Presence of limestone has a pronounced impact on the hydration, being more pronounced for the slags of high alumina content. This is related to the formation of hemi- and mono-carbonate and stabilization of ettringite. Despite of these changes, the pore size distribution is similar among the investigated cements. Thermodynamic modelling matches favorably the experimental data and enables calculating the evolution of the pore volume over the time. A relationship between calculated porosity and compressive strength is proposed and verified. This relationship shows that all hydrated phases have a similar impact on compressive strength and the strength is mainly related to the pore volume.
This study develops an analysis method for estimating the process of corrosion in concrete, including initial corrosion and the onset of corrosion-induced cracking. The method is suitable for application in rationalizing the verification of the durability of salt-damaged RC structures. Corrosion deterioration is computed by coupling the analysis of structure with the analysis of reinforcement corrosion. A method of calculating macro-cell corrosion in consideration of macro-cell corrosion current density is also proposed, focusing on cathodic elements of a reinforcing bar. The proposed analytical method is validated against dry-wet cyclic tests with salt solution to simulate macro-cell corrosion. We verify the accuracy of the method by confirming the non-uniformity of the concrete before cracking and, by coupling the analysis with structural analysis, investigating how the expansion ratio of corrosion products and diffusion coefficient of chloride ions affect the onset of corrosion, the time of initial corrosion cracking, the chloride ion density and the corrosion amount. This paper is based on an original paper (Suzuki et al. 2014) written in Japanese.
Pull-out tests and numerical analyses for deformed bar were performed on test specimens having cracks in concrete along the axial direction of the bar. The parameters for the experiment and analysis were: the maximum width of the initial crack, the presence or absence of a mechanical anchorage, the presence or absence of bond on either side of the deformed bar, and the presence or absence of a transverse bar. In both the experiments and the analyses, the pull-out load was applied at the end of the deformed bar after introducing the initial cracking by means of preloading. The results showed that the pull-out performance was greatly reduced by cracking along the axial direction of the bar. Also, it was seen that cracking along the deformed bar tended to occur only on one side of the bar. In the particular case of mechanical anchorage it was found that bending stresses occurred near the anchorage due to eccentric loading. The transverse bar increases the residual crack width when the same initial crack width was generated before unloading and also inducing spalling of the concrete cover due to cracking of the bond, resulting the reduction in pull-out strength.
A change in distance between the generator rotor axis and the bearing of the table deck in the turbine generator (TG) foundation of Unit #1 of the Ikata nuclear power plant was observed during an inspection in 1979 after the start of operation. This led to measurements of the structure expansion (from 1981), the cracking condition (from 1982), and core sampling of the concrete member (from 1986), based on which deformation and cracking was determined to be the result of an alkali–silica reaction (ASR). However, as the strength of the TG foundation was still in excess of its design value, ASR was not considered to have affected its ability to support equipment. Subsequent analysis of the structural stability of the TG foundation found no change in deformation or concrete strength over a period of continued monitoring, and hence, the TG foundation has been used up to the present time. The aim of this paper is to establish a maintenance management method for similar structures exhibiting cracks caused by ASR.
This study examined the compressive strength model for cementitious material based on the Portland cement -aluminous cement–anhydrite system, which considers the physical properties of the hydrate and phase composition. The volume fraction of each hydrate and the hardness of the synthesized hydrate measured by nanoindentation were used to determine the calculation formula of σ0 of the Ryshkewitch model. The formula for calculating the k value using the volume fraction of each hydrate was also suggested. In the range of this study, the difference in the compressive strength of this system could be arranged by the Ryshkewitch model using the σ0 and the k values calculated by the suggested calculation formulas.
The influence of temperature and added lime on the dissolution of the glassy phase in a binary blend of low-calcium siliceous fly ash and cement. An XRD-based technique is used for quantification of the glassy phase content and the amorphous reaction products in the binary blend. The experimental technique allows for tracking the formation of amorphous reaction products, the availability of lime and the unreacted glassy content. The rate limiting step in the pozzolanic reaction of low calcium fly ash is established to be the dissolution of its glassy phase. Results indicate that increasing the temperature from 25℃ to 40℃ produces a significant increase in the rate of dissolution of the glassy phase of fly ash and an increase in the rate of formation of reaction products. Addition of quicklime is very effective in producing reactive lime in the solution. The rate of dissolution of the glassy phase of fly ash and the rate of pozzolanic reaction are not significantly influenced by the lime content in the system. The proportion of fly ash which remains unreacted which is indicated by the undissolved glassy phase depends on the availability of lime in the system.
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