## 1 Introduction  
Reactive powder concrete (RPC) is a newly emerging material that is typically composed of cement, silica fume, and sand, along with the use of fibers and superplasticizer. It is characterized by high compressive and tensile strength, low porosity, and high ductility [1]. These properties of RPC are obtained by (i) the suppression of a weak interfacial transition zone (ITZ) that is normally developed around the aggregate through eliminating the coarse aggregate; (ii) the refinement of the hydrated paste microstructure using silica fume (SF) and elevated temperature curing; (iii) the use of superplasticizer (SP) to decrease the water-to-cemertitious material ratio; and (iv) the addition of steel and synthetic microfibers [2; 3; 4]. Unlike ordinary concrete, the replacement of coarse aggregate with fine sand renders a better uniformity of RPC and an enhanced ITZ in RPC. [PERSON] et al. [5] and [PERSON] et al. [6] reported that finely and well-graded quartz sand is typically used instead of using coarse aggregate. The particle size of sand is ranged from 150 \(\upmu\)m to 600 \(\upmu\)m, with a mean value of 250 \(\upmu\)m. The sand particle size smaller than 150 \(\upmu\)m is not used, because it causes interference with the largest cement particles. [PERSON] et al. [7]studied the effects of sand particle size and gradation on the strength of reactive powder concrete. They found that a higher strength of RPC was related to a smaller maximum size and larger packing degree of the sand, because of the enhanced ITZ between the sand and the hardened cement paste. Silica fume (SF) is also incorporated into RPC mixture as a partial replacement of cement. Similar to other supplementary cementitious materials, SF provides a pore refinement effect either by a filler effect or pozzolanic reaction with the calcium hydroxide (CH) produced from the primary hydration of cement. This leads to the improved microstructure of RPC and a higher strength than ordinary concrete [2; 8; 9]. However, an optimum SF content in RPC typically ranged from 10% to 25% by the replacement of cement by mass, resulting in good workability and strength properties [10; 11]. [PERSON] et al. [5] observed that increasing the SF content has a positive effect on the compressive strength and modulus of rupture of RPC only to a certain optimum point, while a further increase of SF content does not result in a significant strength rise in RPC. Another important factor that affects the property of RPC is the curing condition. Generally, RPC is cured in the form of either autoclave curing through applying heat and pressure simultaneously on fresh RPC samples, or high temperature thermal/heat curing using steam curing, hot water bath curing, and hot air curing. Depending on the preset pressure and temperature, a compressive strength of up to 500 MPa was achieved when cured at the autoclave [12; 13; 14; 15]. Under high-temperature thermal curing, silica fume dissolves rapidly, and the rate of reaction between SF and CH led to a high early strength gain of RPC increases [16; 17]. [PERSON] and [PERSON] [18] investigated the effect of different curing regimes (ambient air curing, hot air curing, hot water bath curing, and accelerated curing) and durations on the early strength development of reactive powder concrete. They found that the strength development of RPC is strongly dependent on the temperature and duration of exposure. They also observed that among four different curing methods, hot water bath curing gives higher strength, but the combined curing regime (e.g., hot water curing and hot air curing) shows better compressive strength development than a single curing regime. Changing the water-to-binder ratio (WB) is another important parameter that affects the strength of RPC. Decreasing the WB positively affects both the compressive strength and modulus of rupture of RPC [5]. However, when the WB is decreased beyond a certain limit, the workability of obtained concrete was not sufficient for comfortable handling and placing [8].