Experimental Study on Early-Age Crack of Mass Concrete under the Controlled Temperature History

Nannan Shi,Dahai Huang,Jianshu Ouyang,Runxiao Zhang

doi:10.1155/2014/671795

Abstract

Thermal deformation under restrained conditions often leads to early-age cracking and durability problems in mass concrete structures. It is crucial to monitor accurately the evolution of temperature and thermal stresses. In this paper, experimental studies using temperature stress testing machine (TSTM) are carried out to monitor the generated thermal cracking in mass concrete. Firstly, components and working principle of TSTM were introduced. Cracking temperatures and stress reserves are selected as the main cracking evaluation indicators of TSTM. Furthermore, effects of temperature controlling measures on concrete cracking were quantitatively studied, which consider the concrete placing temperature (before cooling) and cooling rates (after cooling). Moreover, the influence of reinforcement on early-age cracking has been quantitatively analyzed using the TSTM. The experimental results indicate that the crack probability of reinforced concrete (RC) is overestimated. Theoretical calculations proved that the internal stress can transfer from concrete to reinforcement due to creep effect. Finally, the experimental results indicate that the reinforcement can improve the crack resistance of concrete by nearly 30% in the TSTM tests, and the ultimate tensile strain of RC is approximately 105% higher than that of plain concrete with the same mix proportions.

Highlights

Mass concrete structures are often constructed in hydraulic engineering, in which thermal stresses arise due to the cement hydration
Crack resistance represents the ability of concrete to prevent cracking, and enhancing the crack resistance can postpone the moment of concrete cracking
(1) Case 1 showed that the lower cooling rate can reduce the probability of concrete cracking and postpone the concrete cracking, considering that the cracking temperature and the crack reserve of the two tests (Test 1 and tensile strength of Specimen 2 (Test 2)) are (26.11∘C, 17.29∘C) and (1.95%, 30.55%), respectively

Summary

Introduction

Mass concrete structures are often constructed in hydraulic engineering, in which thermal stresses arise due to the cement hydration. The mass concrete, such as columns, beam, lock, pier, or dam, requires special measures of coping with the generation of thermal stress according to the ACI-116 [1]. Some massive reinforced concrete (RC) structures, such as concrete piers, walls, columns, and foundations for large structures, are much smaller than a typical concrete dam. If they are made of high performance concrete, the thermal cracking can be as serious as dams. In the massive RC structures, the roles of reinforcement bars are limiting crack widths [3, 4]

Methods

Results

Conclusion