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 Three types of chemical admixtures and curing regimes were used with ultra-highperformance concrete (UHPC).  150 MPa compressive strength is secured after 72 hours using Hyperplast PC-202 and curing at 90ºC.  UHPC mixtures require high admixture dosages, resulting in prolonged setting time.The types of post-setting curing and high range water reducing (HRWR) admixture used in Ultra-High-Performance Concrete (UHPC) mixtures play significant roles in determining their rheological and mechanical properties. This study compares the performance of three types of HRWR admixtures commercially available when added to UHPC mixtures under three different curing regimes. Mixtures made with the different superplasticizers were evaluated for their flow, 45mins flow retention, and setting time as fresh mix properties. Compressive strength was also tested for each mixture after 3, 7, and 28 days of curing at the investigated various curing regimes. Sika Viscocrete 180GS produced the highest mixture flow and flow retention levels with a 241 mm flow and 93.7% flow retention. Sika Viscocrete 168-1 produced the best results of setting time with 3 hours as compared to 12 hours with Sika Viscocrete 180GS. Using Hyperplast PC-202, the required 150 MPa compressive strength was secured as early as 3 days of curing with a 48hrs-90ºC curing regime. Using the same HRWR admixture, compressive strength values slightly lower than 150 MPa were reached after 7-28 days when the 72hrs-60ºC regime was adopted. The last curing regime was recommended for producing architectural UHPC units to minimize the delayed formation of ettringite.

The combination of fibers with traditional reinforcement may be a very interesting design solution to achieve more durable and economical structures. In this study, a total of seven slabs; six ultra high performance concrete (UHPC) slabs and one normal strength concrete slab were tested previously by the Author to observe the crack spacing and number of cracks in tension area, crack width and absorbed energy. Four slabs of UHPC with steel fiber of 0.5%, one UHPC slab with 1.1% steel fiber and one slab of UHPC without steel fiber were used in the analysis. For UHPC, the contribution of fibers to cracking in terms of crack width and spacing is significant when the amount of fibers increased. Also, normal strength concrete slabs have longer crack spacing as compared with UHPC members.

A good performance of reinforced concrete structures is ensured by the bond between steel and concrete, which makes the materials work together, forming a part of solidarity. The behavior of the bond between the reinforcing bar and the surrounding concrete is significant to evaluate the cracking control in serviceability limit state and load capacity in the ultimate limit state. In this investigation, the bond stresses between reinforcing bar and reactive powder concrete (RPC) was considered to compare it with that of normal strength concrete (NSC). The push-out test with short embedment length is considered in this study to evaluate the bond strength, bond stress-slip relationship, and bond stress-crack width relationship for reactive powder concrete members. The compressive strength of concrete, the nominal diameter of reinforcement, concrete cover, and amount of steel fibers and embedded length of reinforcement were considered as variables in this study. The test results show that the ultimate bond stress increased with increasing of the compressive strength of concrete, decreasing the nominal diameter of the reinforcing bar, increasing the concrete cover and increasing steel fiber content. In a bond stress-slip relationship, the NSC specimen shows a very short softening zone after reaching the peak point in comparisons with RPC specimen. In RPC, bond stress-slip relationship shows stiffer behavior when the steel fiber content was increased. RPC shows stepper softening zone due to the presence of steel fiber, and the absence of steel fiber cause push-out failure without descending part after peak point. Using NSC instead of RPC in anchorage between reinforcement and concrete, decrease the crack width produced due to radial tensile stresses through the push-out of reinforcing bar. In RPC, the absence of steel fiber, decrease the nominal diameter of the reinforcing bar, increase the concrete cover, decrease the embedded length of reinforcing bar cause push-out failure and vice versa cause splitting failure.

The use of high chemical admixture dosages in ultra-high-performance concrete (UHPC) mixtures to achieve adequate water demand can slow down early cement hydration and prolong the setting time. In this study, the effects of nanosilica (Ns) with high chemical admixture dosages on the rheological properties of UHPC was investigated. A factorial design approach was employed to predict and optimise the Ns content, water-binder ratio (W/B), and sand-binder (s/b) ratio to obtain the best flowability, setting time, and compressive strength. This study represents an attempt to modelling and optimise eighteen UHPC mixtures containing various proportions of water, cement, and sand, with the Ns powder as a possible property enhancer to achieve the best rheological properties. Response surface analyses revealed the significant effect of Ns in controlling the prolonged setting time and improving the compressive strength. Based on the applied criterion conditions, the optimisation results indicated two mixtures targeting either the maximum compressive strength or cost effective materials. The use of a 1.12 s/b ratio with a controlling level of 0.8% Ns content was suitable to fulfil the compressive strength, flow, and setting time limit values.