(2) Aggregate gradation is poor. It is mainly manifested in the stone factory that the stone sieve is divided into 5 ~ 10mm, 10 ~ 25mm and 20 ~ 31.5mm and other grade sales, and the concrete enterprise uses alone to cause the gradation difference. In addition, stone factory small corner material stone chips, often as the so-called "mechanism of sand" sales to concrete enterprises, stone chips grading mostly "two particle content is large, insufficient middle particles", to the preparation of concrete to bring difficulties.
(3) The fineness modulus of fine aggregate sand changes greatly. The fineness modulus varies greatly due to the different sources and materials of fine aggregate. Concrete companies often have multiple suppliers of fine aggregate, which cross over the coming materials, exacerbating the fineness modulus fluctuation of fine aggregate.
(4) Poor aggregate material. Aggregate contains a large number of weathered weak particles, resulting in low crushing value, water absorption rate on the high side, on the one hand, resulting in poor performance of concrete mixing, on the other hand, resulting in low concrete strength, poor durability.
(5) aggregate grain shape difference. Influenced by aggregate parent rock material and production technology, the content of needle-flake particles in aggregate is high. Although some particles do not conform to needle-flake specifications, the irregular shape of particles leads to the deterioration of concrete workability and mechanical properties.
Strengthening the detection of sand aggregate is the key to control aggregate quality. To preliminarily determine the quality of fine aggregate, the method of "experience + test" is adopted, with experience as the supplement and test as the main. The empirical method of fine aggregate detection is "watching, kneading, rubbing, throwing and washing" and other methods: "watching", that is, watching the gradation, estimating the degree of thickness and fineness, holding a handful of sand in the palm of the hand, carefully watching whether the thickness and fineness of the sand is evenly distributed, the more uniform the gradation distribution of particles at all levels, the better; "Grasp", grasp a hand to estimate the water content of the sand, grasp to see the state of the sand group, the tighter the sand group proves the higher the water content, the lower the other way round; "Rub", grab a handful of sand in the palm, rub with two palms, gently clap hands, see the adhesion of the palm of the mud layer, the mud layer and yellow proves that the sand contains high mud, on the contrary, low mud; "Throw", the sand is held into a group and thrown in the palm of the hand. If the sand group is not loose, it can be determined that the sand is fine, containing mud or high water content. "Wash", grab a handful of sand in the water to wash it, see the degree of muddy water to determine the mud content, but also see the material and grain shape of the sand particles after washing. The empirical detection of coarse aggregate mainly depends on the intuitive methods such as "seeing and grinding". "Look", that is, look at the particle size distribution, look at the coarse aggregate grain shape, look at the surface impurities and mud content, look at the content of weathered soft particles; And then combined with "grinding", that is, two or more coarse aggregate particles in the hand grinding, judging the hardness of coarse aggregate.
If there is doubt about the quality of the aggregate after preliminary judgment, it should be tested and verified immediately for quantitative analysis.
