Effect of Fly Ash and Activator on Performance of Steam-Cured Concrete

Abstract

In precast concrete elements manufacturing, steam-cured concrete incorporating 30% fly ash encountered the problem of a too low demoulding compressive strength. To resolve it, this paper developed a new steam-cured concrete (AFSC) incorporating fly ash and a chemical activator. Experiments were conducted to investigate the mechanical properties of AFSC. The corresponding mechanism was also discussed by testing the microstructure of concrete. Results indicate that the demoulding compressive strength of AFSC can meet production requirements, and compressive and flexure strength of AFSC at later ages increase well. Compared with that of ordinary steam-cured concrete, AFSC has a higher tensile strength, and the capability of AFSC to resist cracks is enhanced remarkably. At an early age, addition of the chemical activator can distinctly accelerate the extent of hydration of the fly ash cement systems, and thus the microstructure of concrete becomes denser.

Effect of Curing Regime on the Mechanical Properties and Durability of Steam Cured-Concrete

“…Water in concrete diffused from high temperature areas to low temperature areas, resulting in two scenarios: surface moisture migrating to the interior, and water transforming into the gaseous phase. Prolonged static resting times promoted the initial strength of mineral concrete, which impeded the migration of surface moisture to the interior and the transformation of water into the gaseous phase, reduced the volume expansion caused by steam heating, and, thus, inhibited the damage caused by high-temperature steam curing to the internal pore structure of the concrete [46].…”

Short Review on the Application of Recycled Powder in Cement-Based Materials: Preparation, Performance and Activity Excitation

“…The conclusions showed that the effects of activators were CaCl 2 > CaSO 4 •2H 2 O > NaOH, Ca(OH) 2 , and Na 2 SO 4 > no excitation. From the SEM images analysis, it can be found that the mortar without an activator presents a blocky slab and has poor cementing action (Figure 7a); the mortar samples excited by NaOH, Ca(OH) 2 and Na 2 SO 4 activators showed a honeycomb morphology because the ettringite was wrapped and filled with gel [60] (Figure 7b,d); and the samples excited by CaSO 4 •2H 2 O showed a large amount of gel and no acicular ettringite (Figure 7e), which made the microstructure more dense; due to the easy diffusion of Ca 2+ and Cl − and the continuous reaction with active Al 2 O 3 and CaCl 2 , the samples excited by the CaCl 2 activator generated large expansive hydrated calcium chloroaluminate to fill the microscopic pores, which generated gel, ettringite, and rod-like Frediel salt [61] (Figure 7f). The chemical excitation mechanism is mainly through increasing the concentration of OH − in the recycled powder slurry to form free polyunsaturated bonds [62].…”