EFFECT OF EXPOSURE OF CEMENT ON THE COMPRESSIVE STENGTH OF CONCRETE

Abstract

Concrete has become the bedrock of infrastructural civilization in Nigeria as over 75% of the infrastructures in Nigeria have to do with concrete. Most times, Engineers design for a particular grade of concrete and Post-construction checks shows that concrete is defective of this strength and exposure of cement is observed to be one of the causative factors. In this study, the effect of exposure of cement on the compressive strength of concrete was investigated; consequently, determining the behavior of the compressive strength of concrete with different cement exposure time and conditions and also determining the limiting exposure time of cement beyond which cement should not be used in the production of structural concrete; a remedial approach to cement that have been exposure less than or above the limiting exposure time was also an objective. In the experimental work, fresh cement as well as Cement exposed to two basic conditions (Warehouse and Open-Air Exposure) for different durations (6,12,18,24 and 42 Hours) and consequently used in the production of concrete after mix design was carried out for a target strength of 30 N/mm2. Slump Tests and Compressive Tests were carried out on the various samples and it was observed that the strength value of concrete constantly reduces from 29.13N/mm2 for the control sample (No cement Exposure) to 17.28N/mm2 and 13.90N/mm2 for 42 hours cement exposure in Warehouse and Open-Air Exposure conditions respectively. Regression model was also calibrated to predict the Strength of Concrete and the %Loss in strength with increase in exposure duration for the both conditions; this model possessed very high correlation value and thus validated. Furthermore, the limiting exposure value was established to be 16.66 Hours and 10.45 Hours for warehouse and open-air Exposure respectively. In conclusion, it was observed that there is considerable reduction in the compressive strength of concrete with increase in exposure time of cement and that the rate of loss of strength of concrete with exposure duration varied for the different exposure conditions. Also, Remedial analysis for exposed cement was also carried out in order to create an alternative for complete disposal of cement, and an algorithm for this process was illustrated and finally, it was observed the workability of concrete was not affected by the exposure of cement.