Experiments Of Cement Pastes With Circularly Restrained Composite Ring Specimens

Ring test is a simple and efficient way to Testimate the sensitivity of cracking of cement based materials. To make more efficient researches on it,Ta new improved circularly restrained ring test with composite specimens is put forward in this paper,which is used to make sure the crack appears at a special area and to shorten the time of restrained shrinkage cracking of cement based materials such as mortar and concrete.Compared with conventional ring test,composite specimens,which were made up of various volume content of rubber particles in cement pastes,water-cement ratio in different parts,and with four kinds of different sizes of molds,were applied to check out the feasibility of the new method,and make some basic studies on the shrinkage and anti-cracking performance of cement pastes with rubber particles .In this article,compressive strength and flexural strength of cement paste specimens were measured and analyzed. The results showed that the mixture of rubber particles in the cement pastes reduces the compressive strength and flexural strength to some degrees,however,as the volume fraction of rubber particles increases,the flexural strength had a substantial increase in compressive strength. And during the measurement,it was found that,the mixture of rubber particles in the specimens changed the damage form from brittle fracture to ductile fracture.Experiments of composite specimens,with different water-cement ratio,volume content of rubber,angle combinations,and different sizes of molds,were carried on, and the results of the composite ring tests showed that: (1) When the water-cement ratio is the same,as the volume content of rubber particles increases,the cracking time of cement paste ring specimen gets to be longer gradually;(2)While the specimens were composed with two kinds of different cement pastes,whose water-cement ratio were 0.40 and 0.25 and in five different combination of angles,the crack appeared in the area where the water-cement ratio equals 0.25;(3)Adding rubber particles in a certain area of one specimen while the remained part was non-rubber,the crack appeared in the part without rubber particles. Under the conditions of different water-cement ratio and four kinds of different sizes of molds,the same results were given in the experiments;(4)When the same composite specimens were put in different temperature and humidity conditions,the one in lower temperature and higher relative humidity conditions cracked later than the one in higher temperature and lower relative humidity;(5)When the composite specimens with the same water-cement ratio in four different sizes were put under the same environmental conditions,the ones whose inner diameter were thrice size of the previous rings and the height and thickness remained the same as the previous ones,cracked in the shortest time,and then were the previous rings. The rings that had a three times height of previous rings and the same inner diameter and thickness cracked after the previous rings. The ones that were in the size of the same height and the inner diameter but were triple size of thickness than the previous rings,took the longest time to crack.