The influences of metakaolin, w/b ratio and fibers on the properties of green-HFLWC

A new approach to control depletion of natural resources and CO₂ emission during concrete production, lightweight aggregate, low-C₃A cement and supplementary cementitious materials were utilized to develop a green-high strength flowable lightweight concrete (green-HFLWC). The green-HFLWC was developed incorporating low-C₃A cement, metakaolin (MK), fly ash (FA) stalite and silica sand. Effects of metakaolin, w/b ratio and different types of fibers on concrete properties were investigated. The results showed that the green-HFLWC incorporating MK with 0.26 w/b ratio could reach high strength (28-day compressive strength of 89 MPa), high flowability (slump flow of 652 mm) and lightweight (oven-dry density of 1883 kg/m³). In addition, it was found that long polypropylene (LPP) fibers increased the splitting tensile strength of HFLWC by 71 % and reached 136 % of equivalent flexural strength ratio of HFLWC compared to the control mix. Moreover, flexural strength of HFLWC with 2 % volumetric ratio of LPP fiber was better than that of the short polypropylene (SPP). At the same time, the steel-LPP hybrid fibers decreased compressive strength by 56 % compared to the control mix. Also, the water absorption ratio for most of mixes was less than 2 %. Furthermore, the CO₂ emission and cost of each mix were calculated and a new carbon emission intensity index (C_si) is proposed. Considering the excellent mechanical (high specific strength >40, high ductility with fibers) and durability performance (low water absorption ratio <2 %, high carbonation resistance) of green-HFLWC (C_si <12), it is recommended for the future high-rise buildings located in harsh environment.