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Ultra-high-performance concrete (UHPC) has promising applications in civil engineering. However, the elastic modulus of UHPC is relatively low compared with its compressive strength, which may result in insufficient stiffness in service. This work was carried out to explore the feasibility of producing UHPC with high elastic modulus by nano-Al2O3 (NA). Based on particle densely packing theory, the initial mixture of UHPC was designed via the modified Andreasen and Andersen model. An experimental investigation was conducted to systematically examine the effects of NA on different properties of UHPC, including its fluidity, mechanical properties, durability, and microstructure. It was found that: (1) Compared with UHPC without NA, the flexural strength, compressive strength, and elastic modulus of UHPC were improved by 7.38–16.87%, 4.08–20.58%, and 2.89–14.08%, respectively, because of the incorporation of NA; (2) the addition of NA had a prohibiting impact on the threshold pore diameter and porosity of UHPC, which suggested that NA could be conducive to its pore structure; (3) the incorporation of NA led to a decline of 2.9–11.76% in the dry shrinkage of UHPC, which suggested that incorporating NA in a proper amount could reduce the risk of cracking and alleviate the dry shrinkage of UHPC; (4) the optimal amount of NA in UHPC was 1.0%, considering the effects of NA on workability, mechanical properties, microstructure, and the durability of UHPC. [ABSTRACT FROM AUTHOR]

Recently, the use of aeolian sand for producing ultra-high-performance concrete (UHPC) was introduced. Preliminary investigations suggested that it was feasible to use aeolian sand to produce UHPC. In this study, systematic investigations on the workability, hydration, microstructure, and mechanical properties are conducted to unveil the dominant factors controlling the performance of the UHPC produced with aeolian sand. Moreover, an intensive mixing process is also introduced to promote the efficiency of using aeolian sand and steel fibers for producing UHPC. The results show that the UHPCs produced with aeolian sand by an intensive mixing process exhibit substantial improvements in workability, mechanical strength, fiber dispersibility, and porosity, although the degree of cement hydration is only slightly improved. The improvement in the performance of the UHPC is found to be mainly related to the improvement in dispersibility of steel fibers and thus the refinement in the pore structure. [ABSTRACT FROM AUTHOR]

• UHPC with high elastic modulus was designed via MAA particle packing model. • Workability, microstructure, and mechanical strength of HMUHPC were studied. • Elastic modulus of HMUHPC ranged from 40.5 GPa to 49.3 GPa. • Optimal content of steel chips in HMUHPC was 50 wt%. Elastic modulus is one of the key parameters to weigh the stiffness of concrete members and structural design in civil engineering. Despite its excellent performance in durability and mechanical properties, ultra-high performance concrete (UHPC) is featured with relatively low elastic modulus, which prevents UHPC from being applied in a much larger scope. This study was conducted to explore the feasibility of preparing UHPC with high elastic modulus (HMUHPC) by using steel chips. The modified Andreasen and Andersen (MAA) particle packing model was used to design the initial mixture of HMUHPC. Based on this, some steps were followed to investigate the impacts of varying contents of steel chips on HMUHPC with regard to its mechanical properties, workability, and apparent density. In addition, attention was also paid to how steel chips affected the microstructure of HMUHPC and the ultrasonic pulse velocity (UPV) propagated in HMUHPC. It was found that: 1) Due to the addition of steel chips, there was an increase from 9.65% to 21.73%, 6.38% to 15.85%, 1.28% to 10.49%, and 3.11% to 16.44%, respectively, in the elastic modulus, compressive strength, flexural strength, and apparent density of HMUHPC; 2) The addition of steel chips could reduce the porosity of HMUHPC and optimize its pore size distribution; 3) Considering the effects of steel chips on HMUHPC regarding its microstructure, mechanical properties, and workability, the optimal content of steel chips in HMUHPC was 50 wt%. [ABSTRACT FROM AUTHOR]

• UHPC with high elastic modulus was design by MAA particle packing model. • Workability, microstructure, and mechanical strength of HEMUHPC were studied. • Elastic modulus of HEMUHPC ranged from 40.50 GPa to 47.13 GPa. • Relationship between elastic modulus and compressive strength was a power function. • Optimal content of alumina micro-powder in HEMUHPC was 10%. Elastic modulus is an important parameter in engineering structural design for evaluating the stiffness of concrete members. Ultra-high-performance concrete (UHPC) has excellent mechanical properties and durability, but the relatively low elastic modulus prohibits the widespread use of the UHPC. In this study, high elastic modulus UHPC (HEMUHPC) was designed according to Modified Andreasen and Andersen particle packing model proposed by Funk and Dinger. Effects of alumina micro-powder (the content of alumina is higher than 99%, and the particle size is lower than 100 μ m) on the workability, microstructure, and mechanical properties of HEMUHPC were systematically investigated. The reason for the improvement of elastic modulus of HEMUHPC was revealed by nano indentation test. It was found that, 1) the porosity and threshold pore diameter of HEMUHPC were reduced because of the addition of alumina micro-powder; 2) the flexural strength, compressive strength, and elastic modulus of HEMUHPC were increased by 3.54–11.23%, 8.89–22.83%, and 6.19–16.37%, respectively, due to the addition of alumina micro-powder; 3) the optimal content of alumina micro-powder was 10%, considering its effects on the workability, mechanical properties, and microstructure of HEMUHPC; 4) Nano indentation experiments showed that the elastic modulus of the alumina micro-powder was 90–135 GPa, which is much higher than the elastic modulus of hydration products of HEMUHPC, and thus the elastic modulus of the HEMUHPC matrix could be improved, due to the addition of alumina micro-powder. [ABSTRACT FROM AUTHOR]