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  • Le et al studied the effect of different

    2020-07-31

    Le et al. [2] studied the effect of different types of pores in the performance of the RHA- and SF-modified mortar paste. Both macroporous (particle size: >50 nm) and mesoporous (particle size: 2–50 nm) RHA particles were used in this study. It was observed that the pore size distribution of RHA significantly influenced the pore volume, specific surface area, and water demand of RHA-modified concrete. The authors reported the improved rheological properties of RHA mortar paste due to the incorporation of finer RHA at higher content. A follow-up study by Le et al. [4] attempted to assess the performance and ASR mitigation capability of RHA and SF in self-compacting high-performance concrete. The authors used both reactive (i.e., greywacke sand) and non-reactive (i.e., basalt sand) AZD2858 mg in preparing mortar bars. Three different sizes (5.7 µm, 7.7 µm, and 15.6 µm) of RHA samples were incorporated into this study. It was reported that the finer RHA had higher pozzolanic activity than the coarser one since the finer RHA containing mortar bars exhibited better refinement of pores than the coarser RHA-modified mortar bars. Higher ASR expansion and substantial cracking were observed in the case of mortar bars containing coarser RHA (15.6 µm) and non-reactive aggregates compared to the control specimen. The authors suspected that the excessive expansion was due to the formation of ASR gel inside the RHA particle, which was identified in the energy-dispersive X-ray (EDX) spectroscopy analysis. It was also mentioned that the ASR reactions occurred in mortar bars faster than the pozzolanic reaction of RHA. The main objective of the present study is to observe the effect of RHA size (gradation) and percentage of dosage of local RHA as SCM in concrete to mitigate ASR. The ASR test was conducted according to ASTM C1260 and ASTM C1567 method to observe the expansion phenomenon of RHA modified mortar bars. Three types of graded RHA along with Class C fly ash (CFA) were used throughout the research. CFA and each type of RHA were used separately in mortar bars at two different replacement levels (10% and 20%) by weight of cement for the same curing period of 14 days.
    Material and methods Type-I Ordinary Portland Cement (OPC) and stone sand of fineness modulus (FM) 2.6 were used to prepare mortar bars. Three types of RHA of different gradation were used separately that have particle size 600 µm, 150 µm and 44 µm, respectively (Fig. C.1). None of the SCMs were mixed with each other since they were used independently in preparing mortar bars. The mortar bars prepared using 600 µm RHA, 150 µm RHA, 44 µm RHA and CFA would be termed as 600-RHA, 150-RHA, 44-RHA, and CFA modified mortar bars, respectively in this study. The 600-RHA and 150-RHA were collected from Riceland Food, Inc. Usually, they produce 600-RHA as a by-product of the milling process. It is black in color and very coarse in size. It was further ground to produce 150-RHA. It is finer than 600-RHA and also black in color. But none of these meet AASHTO 321-04 specifications. However, 44-RHA was collected from a commercial industry, Agrilectric, California, and it is gray in color and meets AASHTO M 321–04 specifications. CFA was collected from a local supplier, Charah, Inc. (Fig. C.1.d). The chemical properties of RHA and CFA are shown in Table B.1.