Optimization of Concrete strength using local aggregates from the Eastern Province of Saudi Arabia

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Saudi Digital Library
In the Eastern region of Saudi Arabia on the Arabian Gulf, concrete has been typically quite low in strength and of poor quality. This is attributed to a variety of reasons. The coarse aggregates used in that area in making concrete is mainly obtained from crushing limestone and dolomite rocks that vary appreciably in quality and strength from one quarry to another. Many of the aggregates used are very weak in strength and come from friable chalky rocks that have poor soundness and abrasion characteristics. Also, the fine aggregates, i.e., sand in the area is typically very fine and mainly monogranular. In addition to the above factors, lack of quality control, poor workmanship, no gradation nor washing of the coarse aggregates and no control on the amount of water used in the mix, aggravate the problem. The 28 days compressive strength of concrete that is usually obtained in the area is 2500 psi, maximum. In view of the above, an experimental two-pronged research program was conducted seeking to obtain the best aggregates available in the area and then to optimize the concrete strength using the selected aggregate and other local materials. Improving the quality and hence the strength of concrete is of paramount importance in this area considering the extreme changes in temperature and humidity that affects the concrete adversely. In addition, high strength concrete is required for the prestressed-precast industry that is developing in the area to alleviate the housing shortage in a rapidly growing country. Research performed showed a wide range of available aggregates. Their quality varied from poor to sound and hard aggregates. Incorporation of good quality aggregates, a good mix design, use of admixtures, following the recommended practice for producing high strength concrete led to a remarkable increase in concrete strength. Concrete with 28-days compressive strength of 6000 to 8000 psi was achieved. These strengths were achieved by using conventional concrete materials and practices with emphasis on the following: 1) Selecting good quality aggregates, 2) Washing the aggregates, 3) Finding the optimum maximum size for coarse aggregate, 4) Grading the aggregates within the ASTM C33 limits, 5) Using selective fine aggregates, 6) High cement factor up to 10 sacks per cubic yard, 7) Low water cement ratios (0.35), 8) The use of admixtures to improve workability without requiring additional water, 9) Optimize the fine aggregate to coarse aggregate ratio, and 10) Thorough mixing and vibration.