Effect of Fly Ash Content on the Microstructure and Strength of Concrete under Freeze–Thaw Condition

Abstract

To understand the influence of fly ash (FA) content on the microstructure and strength of concrete under freeze–thaw cycles (FTCs), four groups of concrete with different FA contents (0–30%) were tested under FTC condition. Mass loss rate, relative dynamic modulus of elasticity (RDME), splitting tensile strength and other damage indicators were selected to describe the impact of macro properties. The micro physical changes, porosity and pore size distribution parameters were obtained through scanning electron microscope (SEM) and nuclear magnetic resonance (NMR) experiments. The influence mechanism of FA content on the frost resistance durability of concrete under FTC was discussed from the macro and micro perspectives. The results show that under the action of FTC, the addition of FA fills the pores, reduces the pore spacing, improves the strength of concrete, and makes the RDEM and splitting tensile strength of concrete increase first and then decrease. Among them, 20% FA concrete has the best frost resistance. The pore structure parameters show that the content of pores smaller than 100 nm has a great impact on the frost resistance durability of FA concrete, and increasing the content of these pores can improve the frost resistance durability of concrete.

Study on the Frost Resistance of Composite Limestone Powder Concrete against Coupling Effects of Sulfate Freeze–Thaw

“…Among them, the mass losses of specimens A, B, and C decrease first and then increase during the water freezing cycles. This is because the quality of the water absorbed by the concrete is greater than the quality of the peeling mortar on its surface, which leads to an increase in the early quality of the specimen during the freeze-thaw cycle [15,37].…”

“…(1) The relative dynamic elastic modulus of concrete specimens is related to the density of its internal structure [15,37]. Limestone powder has a certain filling effect at the physical level, which can optimize the particle gradation of the cementitious material system.…”

“…The frost resistance of concrete is closely related to its pore structure [15,39]. In this study, due to the consideration of the cost of the test, only the samples of each concrete formula at the age of 28 d were selected for the MIP test.…”

“…Studies have shown that limestone powder can play a role in filling, nucleation, chemistry, and dilution in concrete [10][11][12][13][14]. Fly ash and slag have certain pozzolanic effects on concrete [15,16]. Different types of mineral admixtures are mixed into concrete in proportion to realize the effective and reasonable matching of different particle sizes, different shapes, and different activities, so as to achieve the complementary purpose of the morphological effect, activity effect, and microaggregate effect.…”

Mechanical Analysis of Fly Ash-Based Light Transmitting Concrete by using Optical Fiber

“…Not only does fly ash offer tangible benefits in terms of mechanical properties and durability, but it also helps alleviate the environmental burden associated with cement production. By partially replacing cement with fly ash, construction practitioners can significantly reduce carbon emissions, curb resource depletion, and mitigate waste generation [19,20]. The journey towards sustainable construction practices encompasses a diverse array of research endeavors, ranging from the optimization of green concrete formulations to the exploration of high-volume fly ash concrete.…”