Abstract
The properties of roller compacted concrete (RCC) with high dosage low quality fly ash are investigated, including strength, elastic modulus, ultimate tensile strain, drying shrinkage, autogenous deformation and durability, meanwhile the microstructure of the same paste containing low quality fly ash and ground low quality fly ash are studied, too. The properties of RCC containing 60% or more ground fly ash meet the design requirement. The microstructure is also tested by using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry-differential thermal analysis (TG-DTA) and Mercury Intrusion Porosimetry (MIP). The results indicate that ground fly ash plays the role of active component besides the physical filling effect at early age, while after 90 days, the surface of the glass beads is erroded and a lot of calcium silicate hydrate and calcium hydroxide staggered as storied dense structure. Low quality fly ash can accelerate the formation of hydration products, resulting in higher degree of cement hydration and denser microstructure, while the hydration heat in total is reduced. At the age of 90 days, fly ash has significant chemical activity and the properties of RCC will be improved at the later stage.DOI: http://dx.doi.org/10.5755/j01.ms.23.3.16318
Highlights
Cement consumption in China has accounted for more than half of the global production
The results indicated that compressive strength of roller compacted concrete (RCC) is relative low at early age 7 days, while it tends to grow appreciably at later ages
At early age, the influence of fly ash on the hydration is mainly related to the “filler effect” [5], the positive effect of “filler effect” may not compensate the negative effect caused by sharp reduction of cement, strength at 7 days is relative low compare to that of later ages
Summary
Cement consumption in China has accounted for more than half of the global production. Since 1970s, the dosage of fly ash used in concrete has increased greatly [1, 2]. In the past three decades, fly ash has always been used in concrete preparation. China is rich in fly ash, and its comprehensive utilization has attracted nationwide attention. The China twelfth-five plan is intended to improve the comprehensive utilization of fly ash to 70 % by the year 2015, and will increase the waste utilization to 60 million tons. Three kinds of RRC, which designed basing on the engineering requirement, are prepared with high volume low quality fly ash firstly. Some mechanisms are studied with aid of micro-test including XRD, TG-DTA, SEM and MIP, the grinding technology is used to improve the hydration properties of low quality fly ash
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