Circulation Fluidized Bed Combustion Fly Ash as Partial Replacement of Fine Aggregates in Roller Compacted Concrete

Abstract

Recently, many people around the world have been concerned with environmental protection and sustainability. The goal of various countries’ research has been focused on how to regenerate existing resources. Circulation fluidized bed combustion (CFBC) technology is one of the emerging combustion technologies for electricity generation and produces more than 800,000 tons of CFBC fly ash (CFA) per year for combustion. CFA has been widely applied in cement additive, new building materials and cement-based materials. The goal of this study was to discuss the engineering properties of roller-compacted concrete containing CFA. Test subjects included compressive strength, flexural strength, absorption, setting time, unit weight, sulfate resistance, SEM microscopic observations and XRD ingredient analysis. Test results indicate the following: (1) using CFA as a substitute of fine aggregates up to 10 wt.% would improve the development of later flexural strength; (2) the increases in pre-pressure would increase the compressive strength and unit weight and decrease absorption; (3) using CFA would reduce the initial setting time by 30%–60% and reduce the final setting time by 16%–20%; (4) using CFA would reduce the absorption; (5) using CFA would reduce the unit weight by 0.5%–2.8%, and the increases in pre-pressure would increase the unit weight by about 0.9%–2.1%; (6) CaO in CFA helps to improve sulfate resistance; (7) scanning electron microscopy (SEM) observation shows that the increases in pre-pressure would reduce the pores; and (8) X-ray diffraction (XRD) analysis shows that the inclusion of CFA would increase the content of Ca(OH)2 in concrete.

Composite Properties of Non-Cement Blended Fiber Composites without Alkali Activator

“…Results of compressive strength development were indicated that S and FA reacted with water and then with calcium hydroxide via a pozzolanic reaction to form hydration products (i.e., calcium silicate hydrate (C-S-H) and/or calcium aluminium silicate hydrate (C-A-S-H) colloids). These findings are consistent with those reported in previous studies [18,24] and it was produced produces viscous hardening behavior in the cementless composites [23].…”

“…By contrast, the shrinkage development curve of specimen S60 was 4 times higher than that of cement mortar, indicating a high SO 3 content following a rapid hydration reaction with a corresponding rapid volume expansion. Previous studies [17,18,24] have also reported on the considerable influence of SO 3 on the strength of mortar specimens containing FA.…”

“…By contrast, the shrinkage development curve of specimen S60 was 4 times higher than that of cement mortar, indicating a high SO3 content following a rapid hydration reaction with a corresponding rapid volume expansion. Previous studies [17,18,24] have also reported on the considerable influence of SO3 on the strength of mortar specimens containing FA. Our results revealed that the addition of fibers to specimen S60 (S60-F1/2/5) did not have a significant effect on shrinkage and the effect of fibers in shrinkage development curves of S40 and S50 specimens were similar to those of S60 specimens.…”

“…Samples were compared with standard Portland cement mortar in terms of mechanical properties, permeability and microstructure. The proposed material is intended to be used as a controlled low-strength material, pervious concrete, reinforced recycled concrete and for other engineering applications [22][23][24].…”

The binding properties of cementitious materials using circulating fluidized bed co-fired fly ash and pulverised coal fly ash

“…The CFFA produced by CFB boilers has a low combustion temperature (850 to 900 degrees Celsius) and limestone is added as a desulphurising agent during the combustion process. Its physical and chemical properties are different from PCFA [10,11,12]. Thus, CFFA cannot be directly used in construction materials in the using the same current technology as PCFA.…”