Experimental Research On The Influence Of Aggregates On The Properties Of Concrete

Aggregates are important composition of concrete. Researchers usually lay research emphasis on cement, water cement ratio, water reducing agents, and active mineral admixtures and so on, but ignore aggregates which take three fourth volume of concrete. With the developing of HPC, the importance of aggregates had been recognized and studied as a highlight. Nevertheless, researches that been done ago lack systematization, and mainly only care about strength of concrete. And the influence of aggregates on workability and durability of concrete is neglected. In fact, geometry character, physical properties and chemical components of aggregates make an important effect on workability of concrete in the early age and mechanical properties and durability of concrete after hardening.With booming of our country's construction, the consumption of concrete increased year by year. Manufactured aggregates are taking the place of traditional natural aggregates step by step to become main component of concrete. However, our country's production quality of aggregates is quit different. Many small factories still manufacture aggregates adopting extension production method, and quality is not stable. This paper belongs to traffic science and technology project in Shandong province named "Study and Control on Manufacturing Technique Indexes of Cement Concrete Aggregate in Shandong Province", and studies the influence of aggregates such as enwrapped by stone power, aggregate's surface properties, volume content, crushed value on properties of concrete. And comparison of manufactured sand and natural sand and concrete properties which is using manufactured sand together with stone power is also studied.The results of studies indicate that coarse aggregates' surface enwrapped by stone power which made and absorbed when production, transportation and storage can cause reduction of concrete strength, and is disadvantageous to the concrete's anti-crack quality at early age .According to "Technical Specification for Construction of Highway Cement Concrete Pavements", continuous grading aggregates with 31.5mm and concrete made by these aggregates are studied, and relations between grading fractal dimension of aggregates D and void ratio p_v and specific value of void ratios D_r are obtained. Using grading fractaldimension of aggregates which is quantitative to characterize properties of aggregates is studied. Small void ratio can obtain high compressive and flexural strength of concrete. The impermeability will be better as the grading fractal dimension is larger. Experiment results show that optimum volume content of aggregates of dense concrete should limit in the range from 0.65 to 0.75. Strength of basalt aggregates concrete is greater than limestone concrete at the same age. And the difference of strength is much larger with the increasing of intensity rank.Test of manufactured sand and natural sand finds that water-absorptivity of fine aggregates has more influence on workability of concrete. Water retention of concrete is better when the water-absorptivity of fine aggregates is larger, and concrete demand more water volume correspondingly. Strength of manufactured sand concrete with good gradation is higher than river sand's concrete strength. By excessively adding manufactured limestone sand with stone power which is collected in the process of sand making, laws and characteristics of workability, compressive, flexural strength, elastic modulus, impermeability, anti-crack properties of concrete with this manufactured sand are found. Using fractal dimension of cracks to evaluate the anti-crack capacity in the slab test is analyzed.