Advanced Materials Research Vol. 857

Abstract: A test method for monitoring of cement mortar quality has been devised and an empirical relational equation between cement mortar fluidity and torque has been worked out. A test method for monitoring of indoor fresh cement concrete quality has been devised and a relational equation between fresh cement concrete and torque has been worked out. A test method for monitoring of fresh cement concrete in a mixing plant has been devised and a relational equation between fresh cement concrete and current property has been worked out. By means of online observed torque and current data, relevant fluidity and slump can be predicted to provide test methods and relevant theoretical basis for intelligent monitoring of fresh cement mortar and cement concrete quality in actual engineering.

Abstract: the influence of mixing amount of mineral admixture, volume content of fine and coarse aggregate have been systematical studied on the workability, mechanical properties and volume stability of self-compacting concrete. Test results showed that with the fly ash content increased, the workability of self-compacting concrete improved significantly, early compressive strength decreased, but increase rate of later strength improved remarkably, and the mixing amount of fly ash inhibited significantly the dry shrinkage of self-compacting concrete; with the volume content of coarse aggregate increased, the workability of self-compacting concrete decreased significantly, but the volume stability of self-compacting concrete improved obviously, thus the optimum volume content of coarse aggregate of self-compacting concrete was range from 0.30 to 0.34; when the volume content of fine aggregate varied at the range of 0.40~0.50, there may be little effects on the workability of self-compacting concrete, but the increase self-compacting concretes volume content could reduce obviously the dry shrinkage of self-compacting concrete. Moreover, the variation in the volume content of coarse and fine aggregate should have slight influence on the early strength of self-compacting concrete, and the influence of the volume content variety on the later strength of self-compacting concrete could be neglected eventually.

Abstract: With respect to the liquefaction behavior of cement concrete material in a vibrational condition, the varying patterns of the vibrational viscosity coefficients, vibrational energy transfer and rheological mechanical behavior of air-entrained concrete and non-air-entrained concrete in a vibrational shear condition were compared by analyzing the vibrational liquefaction processes of concrete. The study has found that the vibrational viscosity coefficient of concrete with air entraining agent added increased notably so that air-entrained concrete can maintain good shuttering behavior during slip-form construction; presence of a large number of tiny bubbles in air-entrained concrete allowed more even transfer of vibrational energy in concrete; and the rheological mechanical behavior of concrete was improved after air entraining agents were added so that it became easier to liquefy by vibration and had better shaping effect upon completion of vibration. Keywords: air-entrained concrete, slip-form construction, cement concrete pavement, vibrational liquefaction

Abstract: In order to improve the durability of concrete structure, studying reduction effect that water-based capillary crystalline waterproofer has on chloride ion diffusion coefficient in the concrete; analyse the inner microstructure of concrete by using electron microscope, and observe the penetration depth of waterproof agent in concrete directly. Research shows that: the water permeable crystalline waterproof agent can significantly reduce the diffusion coefficient of chloride ions in concrete, after concrete forms, the earlier brush waterproof agent, the longer it cure and its improving effect is more prominent after brushing waterproof agent , reduction rate of chloride ion diffusion coefficient in low strength concrete is higher than high-strength concrete;in good condition of water percolation, by detecting of electron microscope, it proved waterproofing agent can penetrate into internal concrete 6cm at least , the gel produced can be filled with pore and micro crack of concrete, so it can significantly improve the compactness of the whole structure.

Abstract: Two methods are used to estimate the concrete strength based upon the maturity concept. The conclusion is that the apparent activation energy E value is key factor in the equivalent age method, larger value of E indicated that the age conversion factor versus temperature function is more nonlinear, and an increase in temperature results in a disproportionate increase in the age conversion factor. It is also shown that there is a unique relationship between maturity and relative strength (ratio of strength to limiting strength), and the relative strength method method-can be used in the prediction for the concrete strength.

Abstract: Combining with the concrete mixing process of twin-shaft mixer, this paper studied the gap-graded concrete mixing uniformity variation under different time. The study found that: under different mixing time, the relative error of coarse aggregate weight in per unit volume decreases, the compressive strength of concrete specimens change from increase to decrease, and they respectively reach the minimum and maximum at 40s, according to this, we get to optimum stirring time is 30~40s; Torque can reflect the condition of concrete mixing to a certain extent, but when the torque becomes stable, it does not stand for the uniformity of concrete mixing, keep stirring about 8s, the concrete mixing will be uniform completely.

Abstract: Effect of fly ash and slag on internal relative humidity (IRH) and dry shrinkage of light weight aggregate concrete (LWC) are studied in this paper. As indicated in this test, mixed with mineral additives can reduce dry shrinkage of concrete. The more volume of fly ash and slag ash, the lower decrease speed of IRH is, which contribute to the decreases of dry shrinkage rate too. At the same curing-age and dosage, the relative humidity inside the fly ash concrete is higher than the slag one. As consequence, the rate of dry shrinkage of fly ash concrete is lower than slag concrete. Also, there is a significant linear correlation between the lowered values of IRH and dry shrinkage rate.

Abstract: This paper analyzed the mechanism of early autogenous shrinkage of concrete, and studied the influence of early autogenous shrinkage of high performance concrete-(HPC) admixed with different kinds of materials of bridge deck pavement. Four different concrete mixes were used: fiber, fiber plus expansive agent, fiber plus fly ash and fiber plus shrinkage-reducing agent. The result shows that the four different mixes can inhibit the autogenous shrinkage of HPC to a certain extent, the inhibitory effect of different mixes in the order of strong to weak is: fiber plus shrinkage-reducing agent, fiber plus fly ash, fiber plus expansive agent, and fiber itself. Furthermore, the inhibition mechanism of each mix was analyzed and a conclusion of mixture of fiber plus fly ash to be the best choice considered of economic and working performance is drawn as well.

Abstract: A new type of small concrete blocks with high strength performance was generated in this study, and the main component of this kind of small blocks were made by the MU15.0 that was extracted from the waste rock chips. The effect of content of stone powder and the different curing methods on the shrinkage of the proposed concrete blocks, was investigated by using the experimental method. The results showed that (i) with the increase of the amount of stone power, the drying shrinkage of rock chips concrete went up at first, and then the opposite change was generated; (ii) The small hollow blocks made by the rock chips concrete after steam curing kiln, under the condition of enough water curing and seal environment, had higher compressive strength and smaller shrinkage comparing with other curing methods.