Assessing the Shrinkage Cracking Potential of Concrete Using Ring Specimens with Different Boundary Conditions

Early-age cracking due to restrained shrinkage affects the performance and service life of concrete structures. Recent studies are successfully making use of the free ring shrinkage test in conjunction with restrained shrinkage measurements for the evaluation of the cracking potential of cementitious materials. This study provides information to improve the interpretation of cracking in ring specimens and a theoretical approach for predicting the stress rate of thick ring specimens. Results show that the rate of strain development and the age-at-cracking vary with specimen drying direction and the exchange surface-to-volume ratio. The results further revealed that early-age shrinkage cracking depends more on the shrinkage rate than the magnitude of the shrinkage itself. Also, it was found that although the restrained ring specimens attained approximately similar strain levels, the cracking age varies significantly, suggesting that elastic stress-strength analysis alone may be inadequate for predicting early-age cracking due to the contribution of creep-relaxation phenomena.

Effects of Rubber Size on the Cracking Resistance of Rubberized Mortars

This study investigated the cracking resistance of rubberized cement-based mortars. Three rubber particle sizes were used: Rubber A (major particle size 2–4 mm), Rubber B (major particle size 1–3 mm), and Rubber C (major particle size 0–2 mm). Traditional restrained ring shrinkage test (RRST), new restrained squared eccentric ring shrinkage test (RSERST), mechanical test, and scanning electron microscopy test were conducted. Results showed that the cracking inhibitory effect of Rubber B was the highest among the three rubber particle sizes. SEM results revealed that the particle size of the rubber does not have much effect on the ITZ (interfacial transition zone) position of rubber and cement paste. For the strength differences of the three types of rubberized mortar, it is mainly because the specific surface area increased as the rubber size decreased, which lead to more ITZ positions and pore structures. Our study verified that RSERST can predict the cracking position and shorten the test period. Compared with RRST, RSERST can also increase the restriction degree. K R is defined as the intensification factor of RSERST restriction degree. The average intensification factor is K R ¯ = 1.17 .

Effect of fly ash on shrinkage of self-compacting concrete using restrained ring test

In recent years, fly ash (FA) has been increasingly used widespread like a mineral admixture for the production of concrete in general and self-compacting concrete (SCC) in particular. Fly ash is an industrial by-product and is generated during the combustion of coal for energy production from the thermal power station. Fly ash is utilized to increase the workability of concrete mixtures and increase shrinkage resistance of the self-compacting concrete. In this paper, the mixture design of the self-compacting concrete with strength grade of 60 MPa is performed with requirement that the workability satisfies the slump flow, T500 and the V-Funnel TV test range from 650 to 800 mm, from 2 to 5 s and from 6 to 12 s, respectively. Besides, fly ash is used to replace cement with content of 15%, 25%, 35% and 50% to evaluate shrinkage resistance. The obtained results showed that using fly ash contents from 25% to 35% to replace cement can ensure workability of the mixture together with high degree of shrinkage restraint. According to ASTM C1581, the evaluation of restrained shrinkage of the self-compacting concrete based on the restrained ring test, this method reduces the testing time but still ensure the reliability. Keywords: fly ash; self-compacting concrete; shrinkage resistance; restrained ring test.

Experimental Study on Anchorage Performance of Steel Bars with FRP Confined Rings

In order to study the performance of reinforcement anchorage connection with FRP restrained ring, static tensile tests were carried out on 66 specimens, The main parameters considered in the test such as the diameter of steel bars, the diameter and thickness of the restraint ring, the strength of concrete and the length of anchorage. The result shows that the anchorage performance of the steel bar can still be guaranteed even if the anchorage length reaches 0.8la, There is no slip and local destruction phenomenon between FRP restraint ring and internal grouting material and peripheral concrete. The study conclusions also indirectly prove that the proposed technique is a reinforcement connection method for fabricated concrete structures with many good performances including the reliable performance, simple construction process and good economic benefit, which is suitable for construction industrialization of prefabricated reinforced concrete structures..