This paper presents the regression equation for predicting compressive strength of in-situ concrete. For this purpose, this study used the data of mixture proportions of ready-mixed concrete and test results of compressive strength at construction sites.This study used 1442 compressive strength test results obtained from the specimens having 59 different kinds of mixtures with specified compressive strength of 18~27MPa, water-cement ratio of 0.39~0.62, maximum aggregate size of 25mm, and slump of 12~15cm.Principal factors that influence compressive strength of concrete are selected by a correlation analysis, and then the multiple linear regression analysis is carried out for predicting compressive strength according to water-cement ratio or cement-water ratio, cement contents and cement-aggregate ratio.

The degradation of the load-bearing capacity of reinforced concrete beams due to corrosion has a profoundly negative impact on the structural safety and integrity of a structure. The literature is limited with regard to models of bond characteristics that relate to the reinforcement corrosion percentage. In this study, uniaxial tensile tests were conducted on specimens with irregular corrosion of their reinforced concrete. The development of cracks in the corroded area was found to be dependent on the level of corrosion, and transverse cracks developed due to tensile loading. Based on this crack development, the average stress versus deformation in the rebar and concrete could be determined experimentally and numerically. The results, determined via finite element analysis, were calibrated using the experimental results. In addition, bond elements for reinforced concrete with corrosion are proposed in this paper along with a relationship between the shear stiffness and corrosion level of rebar.

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This research was performed through the experimental design to get the statistical analysis on foamed concrete mixed plaster with hydrogen peroxide. In this experiment, we set the ratio of each material, which part of lightweight concrete, as experimental factors and evaluated on the mechanical properties by statistical analysis for response variables obtained from experiments. Experimental factors are plaster replacement, water binder ratio, and hydrogen peroxide ratio. Response variables are dry density, compressive strength, and flexural strength. Mixing design of the foamed concrete set up a total of 15 experimental points by Box-Behnken (BB) method of the response surface analysis. Thus, the results of a study were summarized as follows. Values of the probability in experimental factors (plaster replacement, water binder ratio and hydrogen peroxide ratio) on the response variables were estimated to be significant at the 95% of confidence limit. On response surface analysis for dry density of foamed concrete, water binder ratio and hydrogen peroxide ratio were estimated to be significant (α = 0.05), and the relationship between the amount of void and the water content for dry density is inverse proportional. On response surface analysis for the compressive strength of foamed concrete, water binder ratio, hydrogen peroxide ratio and (hydrogen peroxide ratio) 2 was estimated to be significant (α = 0.05). On response surface analysis for the flexural strength of foamed concrete, water binder ratio, hydrogen peroxide ratio was estimated to be significant (α = 0.05). Through multi response surface analysis, we found the optimal area that meets performance goals.