High strength flowable lightweight concrete incorporating low C3A cement, silica fume, stalite and macro-polyfelin polymer fibres

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• HFLWC was developed (strength > 100 MPa, slump flow > 650 mm, density < 2000 kg/m 3 ). • Low C3A cement was used to increase all properties of LWC with low w/b ratio. • A modified model was proposed to predict the compressive strength. • MPP fibres were used to increase the ductility and flexural toughness. Lightweight concrete (LWC) can reduce the self-weight of structures and can save material and labour costs in industry. Despite these merits, the application of lightweight concrete is mostly limited because of low compressive strength, often <60 MPa; and low workability, due to high absorption capacity and possibility of aggregates floating in the case of high water to binder ratio. In this paper, an innovative lightweight concrete was developed with high compressive strength (>90 MPa) and high workability (slump flow value > 550 mm). The workability, mechanical properties, durability, microstructure and aggregates distribution of the high strength flowable lightweight concrete (HFLWC) were investigated. Key mix parameters were examined including Portland and low C 3 A cements, fly ash (FA), undensified silica fume (UDSF), river sand and silica sand. Stalite was used as a high performance lightweight coarse aggregate. In addition, four volume fractions of macro-polyfelin polymer fibres (MPP), 0.5%, 1%, 1.5% and 2%, were added to investigate the effect on the flexure strength and different durability indicators. It was found that the incorporation of stalite, low w/b ratio, low C 3 A cement and UDSF can produce LWC with exceptional strength and flowability. The results showed that HFLWC could be produced with density <2000 kg/m 3 , slump flow of 750 mm, compressive strength of 98 MPa at 28 days and 105 MPa at 56 days. In addition, ductility was improved more than fourfold by increasing MPP from 0.5% to 2%. And new hydration and strength models were developed based on hardened concrete test results and were found suitable for HFLWC. The SEM results showed that the ITZ between the non-pre-treated stalite and the matrix was extremely fine and very dense.