Study on Durability and Pore Characteristics of Concrete under Salt Freezing Environment

Abstract

The macroscopic mechanical properties and frost resistance durability of concrete are closely related to the changes in the internal pore structure. In this study, the two-dimensional and three-dimensional ICT (Industrial Computerized Tomography) pore characteristics of C30 concrete specimens before and after freezing and thawing in clean water, 5 wt.% NaCl, 5 wt.% CaCl2, and 5 wt.% CH3COOK solution environments are obtained through concrete frost resistance durability test and ICT scanning technology. The effects of pore structure changes on concrete frost resistance, durability, and compressive strength mechanical properties after freezing and thawing cycles in different salt solution environments are analyzed. This paper provides new means and ideas for the study of concrete pores. The results show that with the increase in the freezing and thawing times, the concrete porosity, two-dimensional pore area, three-dimensional pore volume, and pore number generally increase in any solution environment, resulting in the loss of concrete compressive strength, mortar spalling, and the decrease in the relative dynamic elastic modulus. Among them, the CH3COOK solution has the least influence on the concrete pore changes; the NaCl solution has the greatest influence on the change in the concrete internal porosity. The damage of CaCl2 solution to concrete is second only to the NaCl solution, followed by clean water. The increase in the concrete internal porosity from high to low is NaCl, CaCl2, clean water, and CH3COOK. The change in the pore volume of 0.1 to 1 mm3 after the freeze–thaw cycle is the main factor for reducing concrete strength. The test results have certain guiding value for the selection of deicing salt in engineering.

Influence of Variatropy on the Evaluation of Strength Properties and Structure Formation of Concrete under Freeze-Thaw Cycles

“…Let us consider the obtained results and discuss them from the point of view of the pore structure. As already mentioned by us earlier and confirmed by numerous studies by other authors [31][32][33][34][35][36]56], vibrated concrete with a simple structure has an open porosity and is thus subject to rather facilitated penetration of moisture from the outside, through the outer layer of concrete and, thereby, is at risk of less resistance to freezing and thawing. This is due, firstly, to easier penetration of moisture through the pores in the outer layer, and thus, unclosed porosity creates a capillary structure of concrete, in which, when frozen, the moisture particles contained in the capillaries lead to the destruction of concrete from the inside.…”

“…Porosity parameters "under freezing and thawing conditions are important for assessing the frost resistance of concrete" [31,32]. The porosity of the HCP is divided into several types, namely: the total porosity of the HCP, the porosity of hydrated cement, capillary porosity, open and closed porosity [33,34]. Formulas for calculating all the above types of porosity of the HCP are presented in Table 2.…”

Concrete 3D Printing: Process Parameters for Process Control, Monitoring and Diagnosis in Automation and Construction

“…The combination of high surface-tovolume ratio and dry environment conditions also fosters an undesirable effect [34,35]. Aside from its aesthetic damage, the presence of cracks can increase the likelihood of water seepages and water penetration in the structure, which can cause corrosion in steel reinforcements, and crack propagation may occur from thermal expansion of water in varied environmental conditions, such as saltwater penetration and freeze-thaw cycles [24,[36][37][38][39]. Plastic shrinkage appears to cause interlayer slips and leads to poor interlayer bond strength and structural durability [34].…”

Experimental Evaluation of the Concrete Damage and Pore Characteristics under Salt-Freezing Cycles

“…According to their study, the internal concrete structure becomes loose and flocculent, an increasing number of pores and cracks appear, and the density decreases, which results in a deterioration of the macro-mechanical properties. Zheng et al [12] carried out concrete frost-resistance durability tests and used ICT scanning technology to study the two-dimensional and three-dimensional ICT pore characteristics of concrete specimens before and after freezing and thawing in different solutions. According to their results, with increases in the freezing and thawing times, the concrete porosity, pore area, pore volume, and pore number generally increased in any solution environment inside the concrete structure, resulting in losses in the concrete compressive strength, mortar spalling, and decreases in the relative DEM.…”