Toughness behaviour of high-performance lightweight foamed concrete reinforced with hybrid fibres

Lightweight foamed concrete (LWFC) is a concrete having structural strength with lightweight density and high flowability. High-performance lightweight foamed concrete (HPLWFC) is used in modern concrete technology and intensively in the construction of high-rise buildings, long-span concrete structures, road sub-bases and other applications. The present work deals with the fresh and hardened properties of LWFC. The fresh properties of LWFC are measured with the flow and fresh density tests. The hardened properties tests include compressive strength, flexural strength, flexural toughness, static modulus of elasticity, ultrasonic pulse velocity, water absorption and oven-dry density. In addition, the study focuses mainly on the effect of the fibres added to LWFC mixes. Two types of fibre have been used: glass fibres and polypropylene fibres, and the combination of glass fibres (GF) and polypropylene fibres (PPF) to obtain hybrid fibres (GF+PPF). This study also focuses on the effect of hybrid fibres on the flexural toughness of HPLWFC. Trial mixes have been used to choose the optimum mix. The definition for choosing the best mix depended on three parameters: oven-dry density, flowability and compressive strength. The volume fraction of glass and polypropylene fibres are 0.06, 0.2, 0.4 and 0.6 %, and 0.2, 0.6, 1 and 1.4 % respectively. The percentages of hybrid fibres "GF + PPF" are "0.2 + 0.6", "0.4 + 0.6", "0.2 + 1" and "0.4 + 1" %. The results show that the greatest increments in the compressive and flexural strengths of LWFC are 51 and 21 % respectively due to the use of 0.6 % glass fibres. On the other hand, LWFC reinforced with polypropylene fibres exhibits only a minor increase in compressive, splitting tensile and flexural strengths. The best percentage of hybrid fibres yielding the highest increment in LWFC is "0.4 % GF + 0.6 % PPF". The results of flexural toughness tests indicate that the polypropylene fibres denote a higher efficiency in the flexural toughness than is the case with glass fibres. The flexural toughness results increase with the volume fraction of the fibres. The hybridization shows the best flexural toughness values due to the cooperative work of the glass and polypropylene fibres boost the performance of flexural toughness in pre-crack and post-crack zones. Therefore, the use of 0.4 % GF + 1 % PPF gives the best results in this regard.