No abstract

I. INTRODUCTIONReactive powder concrete (RPC) is the generic name for a class of cementitious composite materials developed by the technical division of Bouygues, laboratory in France in the early 1990's. It is characterized by extremely good physical properties, particularly strength and ductility [1]. RPC is a relatively new cement-based material composed of cement, ultra-fine reactive powder, and high-quality fine aggregate. Through elimination of the coarse aggregates and reducing the water-tocementitious material ratio, RPC has the unique properties of ultra-high compressive strength and excellent durability [2]. RPC is a new generation concrete developed through microstructure enhancement techniques for cementitious materials. As compared to ordinary cementbased materials, the primary improvements of RPC include the particle size homogeneity, porosity, and microstructures [3]. Nowadays, RPC is regarded as a promising material for special pre-stressed and precast concrete members, including those industrial and nuclear waste storage facilities.More and more attention has been paid on the mechanical properties of RPC at room temperature [3], [4], but few studies have been conducted on the residual mechanical properties of RPC after elevated temperatures [5], [6].Most of the previous studies indicated two important components (as key components) for the successful performance of the concrete in fire; the first deals with its essential properties as a construction material, and the second one deals with its functionality in a structure. Concrete was known to be non-combustible with slow rate of heat transfer [7].Many researchers studied the effect of fire on ordinary concrete, reinforced concrete members on exposing such members to high temperatures in special ovens or fire flame. They worked on the strength and deformation properties at elevated temperatures. However, no works were done on the structural behavior of reactive powder concrete (RPC) beam specimens exposed to direct fire flame.

The effect of warm-rolling on the evolution of microstructure and microtexture was investigated in a duplex steel. For this purpose annealed duplex steel plates were cold and warm-rolled up to 90% reduction in thickness at room temperature and at 625°C, respectively. The austenite volume fraction decreased consistently during cold-rolling indicating that austenite was not stable during cold-rolling. In contrast, austenite was found to be very stable during warm-rolling at 625°C. Development of an ultrafine lamellar deformation structure with alternate arrangement of the ferrite and austenite bands could be observed during warm-rolling. A strong pure metal or copper type texture was observed in the austenite in the warm-rolled material in contrast to brass texture developed during cold-rolling. Development of RD (RD//<110>) fiber and ND-fiber (ND//<111>) was observed in ferrite during both cold and warm-rolling. However, the strength of the RD-fiber was much higher as compared to the ND-fiber in ferrite in cold-rolled DSS as compared to the ferrite in warm-rolled DSS.

The increased use of reactive powder concrete (RPC) in concrete structures has attracted attention towards the structural behavior of RPC in fires. This work examines experimentally the performance of RPC and NSC columns subjected to 25% of the ultimate load and exposed to direct fire flame for a period of 30 and 60 min at various temperature levels. The paper aims to evaluate the maximum temperature level and fire duration that can be withstood by this type of concrete columns. The results show that the failure mode of RPC columns without reinforcement is a sudden shear failure, whereas the failure mode of reinforced RPC columns is a crushing failure with rupture of certain ties. The RPC columns at high temperatures spall intensively; additionally, the ultimate strength clearly decreases compared to the NSC columns at the same conditions.

Curing regime was successful in achieving the targeted strengths of SCGPC.• Fresh properties of SCGPC are significantly affected by the addition of steel fiber. • Vf =1% was the maximum fiber content that could be used in producing SCGPC.Self-compacting geopolymer concrete (SCGPC) is a cutting-edge sustainable engineering material in construction that eliminates the need for both compaction and Portland cement. In this study, the impact of various steel fiber content on the workability of SCGPC was investigated. The basic workability features of freshly made SCGPC, such as filling ability, passing ability, and segregation resistance, were assessed by employing slump flow, V-funnel, L-box, and J-ring test techniques. Obtained results showed that all the investigated characteristics of SCGPC have retreated due to the inclusion of steel fibers. Findings presented in this research confirmed that the basic requirements of EFNARC could only be satisfied when Vf ≤ 1.0%.