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Although the most of National Codes of Practices which deal with cracking recommends a limit for crack widths in order to control the risk of corrosion of reinforcement, the research to date has not sufficiently discussed the effect of cracks on carbonation of concrete. Therefore, this study has been carried out to improve the understanding of the effects of cracking on carbonation process. Mortar beams were used to investigate the effect of crack width on carbonation depth under an accelerating neuteralization test.Comparisons were made between the accelerated and exposure test results to evaluate the effect of acceleration on the carbonation depth. Also the influence of various constituents and curing time on carbonation depth was discussed.

Concrete wastes are generally delivered to the landfill sites for disposal. Due to increasing charges of landfill and scarcity of Natural Coarse Aggregate (NCA), recycled concrete aggregate (RCA) derived from concrete wastes is growing interest in construction industry. In the present study, RCA was used as partial and full replacements of NCA to produce durable Self-Compacting Concrete (SCC). Different SCC mixes were produced with RCA substituting 0%, 25%, 50%, 75%, and 100% NCA by weight, 20% MP and 3% admixture. The water to powder (W/P) ratio are variable after adding water absorption to concrete mixes. The effects of RCA on the key fresh properties such as filling ability, passing ability, and segregation resistance of SCC were investigated and the effects of RCA on hardened concrete such as cube and splitting strength , abrasion resistance , Cantabro test and RCPT test to evaluate durability. The test results revealed that the filling ability and passing ability of SCC were improved for all mixes. All mixes of SCC also possessed adequate segregation resistance. In addition, strong correlations were observed for passing ability, and segregation resistance. The test result of hardened concrete revealed that mixes up to 50%RCA gives normal strength and accepted durability. From the overall test results it could be concluded that RCA can be used to produce SCC substituting up to 50% NCA without affecting the key properties of fresh concrete, give normal strength and accepted durability.

This paper is about the impact of the colored pigments on the concrete and its various properties. A number of colored pigments found in the Egyptian markets were used; some of these pigments are made in China and others are made in Germany. The effects of these materials were studied on the fresh and hardened concrete, the consistency studied by slump test, the strengths studied by compressive strength test and the durability studied by abrasion test and permeability test. It is found from this research that colored pigments does not affect in the concrete mechanical properties in a danger way, Colored concrete must constructed with accuracy and with a good experience.