Mineral Additives to Enhance Early-Age Crack Resistance of Concrete under a Large-Temperature-Difference Environment

Jinjun Guo,Zheng Zhang,Qingxin Meng,Jingjiang Wu,Liyan Cui,Kun Wang,Hao Li,Gefei Qin,Hongyin Xu,Yong Zhang

doi:10.3390/app11199338

Abstract

The large temperature difference condition in Northwest China threatens a myriad of concrete structures during construction, with the daily temperature varying by around 40 °C. To investigate the macro-mechanical properties and microstructural characteristics of concrete containing different amounts of mineral admixtures under such harsh conditions, this investigation used an environmental chamber to simulate a saline soil erosion environment with a large temperature difference. Four types of concrete containing different proportions of fly ash and slag were prepared and exposed in the environmental chamber with a daily temperature change of −5~40 °C to investigate their compressive strength, flexural strength, and fracture properties. Moreover, the X-ray diffraction (XRD) characteristics, microscopic morphological characteristics, pore structure characteristics, and post-erosion chloride ion distribution characteristics were also observed and recorded. Results showed that the mineral admixture could improve the early strength development of the concrete and effectively improve the fracture performance of the concrete. The average compressive strength growth rate of concrete from day 3 to day 14 was 83.25% higher than that of ordinary concrete (OC) when 15% fly ash and 15% slag were added. In addition, the fracture energy of the concrete was maximized when 15% fly ash and 20% slag were added, which was 50.67% higher than that of OC; furthermore, the internal compactness and pore structure were optimized, and the resistance to saline soil erosion was strong. This provides a basis for the practical application of compounded mineral admixture-modified concrete in an arid environment with a large temperature difference and saline soil erosion.

Highlights

Since the implementation of the “Western Development Strategy” and the “One Belt, One Road” initiative, infrastructure construction in the western part of China has been developing rapidly
At day 3 of curing, the compressive strength of the four groups of concrete was ranked from largest to smallest as ordinary concrete (OC) > F15S15 > F10S20 > F15S20, which showed that the OC group hydrated faster and had high initial strength, and as the total amount of mineral admixture increased, the strength of the concrete became lower, which was because the mineral admixtures were not active initially and the strength of the concrete was mainly provided by the hydration of the cement
At the age of day 28, the compressive strength of the F10S20 group, F15S15 group, and F15S20 group accounted for 87.2%, 91.6%, and 90.6% of the compressive strength of the OC group, respectively, but was still greater than 45 MPa, indicating that concrete mixed with 30% to 35% mineral admixture in an environment with a large temperature difference and saline soil erosion would reduce the initial compressive strength of the concrete, but the reduction was not significant, and the strength of the concrete modified by mineral admixtures was expected to exceed that of the ordinary concrete because of the subsequent volcanic ash effect of the mineral admixtures

Summary

Introduction

Since the implementation of the “Western Development Strategy” and the “One Belt, One Road” initiative, infrastructure construction in the western part of China has been developing rapidly. The natural environment in the western region of China is complex and harsh, compared with mild climate areas, and there is a large temperature difference between day and night (the temperature difference between day and night in Xinjiang was previously close to 40 ◦C), low humidity, dryness, and other characteristics [1], which is not conducive to the development of concrete strength and durability. In dry and low humidity environments, early drying of concrete adversely affects the strength, impermeability, and durability of concrete. The early heating during the hydration of concrete is affected by large changes in temperature [5], generating uneven temperature stresses, and as the temperature difference increases, the concrete becomes more susceptible to cracking [6,7] and its mechanical properties decrease as the number of cycles with a large temperature differences increases [8]. As concrete has initial defects such as initial cracks and pores, aggressive ions from the environment enter the concrete interior, causing corrosion of reinforcements and producing expansive defects causing concrete cracking [11,12], which affect the durability and safety of concrete structures

Methods

Results

Conclusion