Papers by Author: Yin Bai

Abstract: Alkali-aggregate reaction is one of the most serious concrete durability problems threating the safety of dam. Some accelerated test methods with high temperature and high alkalinity are usually used in laboratory to evaluate the reactivity of aggregates or the effectiveness of suppression measures. In this paper, an outdoor field exposure station was built to objectively assess the damage risk of real dam concrete suffering alkali-silica reaction. 25 concrete blocks measuring 450 by 450 by 450 mm in size were tested at first stage, all immersed into water to simulate the environment of dam concrete. The influences of the size of aggregate and the amount of cementing materials were tested at the same time. After 7 years field exposure testing, the results showed that: the crack risk of blocks was not proportional to the expansion rates, but influenced by the maximum diameter of aggregate. The block with bigger aggregate had smaller expansion rate, but cracked more easily. If the sizes of aggregate were the same, less cementing materials would cause bigger expansion. The constraint effect is bigger than the effect of alkali content increasing caused by increasing the amount of cementing materials.

Abstract: The machanisms of suspended load abrasion and bed load abrasion are different, but they are not distinguished in the current test methods to evaluate the abrasion resistance of concrete. The abrasion resistance to bed load can be tested by underwater method, and to bed load can be tested by ring speciman method. To study the influence of mixture parameters of concrete to these two machanisms, concretes with different aggregates, different dosage of fly ash and different strength grade were tested by high speed underwater method and high speed ring speciman method. The results showed that the amount of cementing materials and the types of fine aggregate had a significant effect on the high-speed ring specimen method, but it wasn’t affected by the class of strength, so this method only reflected the abrasion resistance of the outer concrete and was easily influenced by the quality of concrete surface; high-speed underwater method was just only related to the types of aggregate, and had little effect on the rest, so it could reflect the abrasion resistance of the inner concrete without caring about the quality of concrete surface. Therefore, choosing different test methods for evaluating the abrasion resistance of concrete should be based on the actual condition in the projects.

Abstract: The temperature-stress testing machine can be adopted to evaluate the crack resistance of concrete, but because of the disadvantages of long time, costs much restrict the development of temperature-stress test method. Getting needed mechanical and thermal parameters by the test here, then be used in the temperature history calculated by simulation software to compare crack resistance of different concretes. By using the convenient method, we can compare crack resistance of different concretes under the actual condition through simulation. The results showed that: the B4Cast simulation software can be used to get different concrete internal temperature histories under different temperature control methods, using the temperature history close to the real condition can evaluate the crack resistance of concrete objectively; on the basis of the temperature-stress test results, via fitting obtained the rules of concrete coefficient of thermal expansion, contraction deformation, elastic modulus, tensile strength and other parameters with maturation changes, then be used in the temperature history calculated by B4Cast, the concrete cracking risk can be simulation analyzed; using this method to compare the same strength grade of normal and pump concrete, the result showed that crack resistance of normal concrete is better.