Ultra-high-performance concrete (UHPC) is a type of cement-based composite for new construction and/or restoration of existing structures to extend service life. UHPC features superior workability, mechanical properties, and durability compared with conventional concrete. However, some challenges limit the wider application of UHPC, such as low workability for large-volume production, high autogenous shrinkage, insufficient flexural/tensile properties, and unpredictable durability after concrete cracking. Therefore, this paper reviews the state-of-the-art technologies for developing UHPC mixtures with improved properties. This review covers the following aspects: (1) the existing design methodologies; (2) the typical ingredients (e.g., binders, aggregates, chemical admixtures, and fibers) for preparation of UHPC and the underlying working principals; (3) the technologies for improving and controlling key properties (e.g., workability, autogenous shrinkage, compressive performance, tensile/flexural properties, and durability); and (4) the representative successful applications. This review is expected to advance the fundamental knowledge of UHPC and promote further research and applications of UHPC.

New development of ultra-high-performance concrete (UHPC)

In corrosion environment, corrosion ions can easily penetrate from the surface into the inside of the concrete due to the porous structure of the surface; in this case, concrete can inevitably suffer from the damage. In this study, an attempt to use nano SiO2 (NS) and silica fume (SF) modifying cement mortar as a Surface Protection Material (SPM) was made, in order to promote penetration resistance of the whole system. SPM was coated on the surface of matrix, and then interfacial bond strength between matrix and SPM was measured; shrinkage consistency was also considered; the chloride penetrability of the system was examined as well. To reveal the mechanism, effect of NS and SF on pore structure, Interfacial Transition Zone (ITZ), hydration process, and compressive strength of SPM were investigated. The results show that matrix coated with SPM on the surface has a good integrity, with excellent interfacial bond strength and little difference in shrinkage, and chloride diffusion coefficient of the system was considerably declined, in comparison with the matrix, showing an excellent penetration resistance. The mechanism behind is that SPM, which was modified with SF-NS, shows the excellent impermeability, and this kind of material existing on the surface can noticeably obstruct the chloride ions penetrating into the inside. In cement hydration process, SF and NS can not only consume a large amount of CH to form dense C-S-H, but also exert the grading filling effect, resulting in the decline in porosity, the increase in density, the improvement in microstructure of ITZ, and the enhancement in mechanical performance. The findings can provide useful experience for the design of the cement-based materials servicing in high corrosion environment.

Nano-silica and silica fume modified cement mortar used as Surface Protection Material to enhance the impermeability

Comparison between the effects of phosphorous slag and fly ash on the C-S-H structure, long-term hydration heat and volume deformation of cement-based materials

In this study, the super-fine ground granulated blast furnace slag was obtained by wet grinding (i.e. WGBBS), and an attempt to activate the super-fine ground granulated blast furnace slag by sodium sulfate (SS) and sodium carbonate (SC) was made. SS/SC-activated WGGBS samples were prepared and cured at the room temperature. The compressive strength at the age of 3 d, 7 d, 28 d, and 56 d was tested. Hydration heat was assessed, and micro structure and hydrates were also characterized with XRD, TG-DTG, SEM-EDS, and NMR; the pore structure was assessed with MIP. The results showed that SS and SC efficiently activated the hydration of WGGBS with D50 = 3.87 μm at the room temperature, and such high activating efficiency of SS and SC under room temperature was seldom reported in the literature. The mechanism behind was mainly because of the super-fine particles of slag with greater amounts of hydration points, which were produced in the process of wet grinding. Difference in activating efficiency between SS and SC was mainly because the anionic groups acted as different roles in hydration process: SS could induce the formation of ettringite while SC could induce the formation of calcite. Such results were expected to provide guidance on designing weak base-activated slag system.

Compressive strength and hydration process of wet-grinded granulated blast-furnace slag activated by sodium sulfate and sodium carbonate

A new hydration model of OPC [1, 2] was used in this study. The quantities of hydration products were calculated for saturated state hydration and for samples that have been dried to 11% rh after hydration. The chloride binding of several hydrated phases (C-S-H, monosulfate, hydroxy-AFm, AFt, CH, and Friedel's salt) has been studied and estimated in relation to the chloride content of the pore solution. Combining two new isotherms, for C-S-H and AFm chloride binding in hardened cement paste, and the computed quantities of all hydration products, a new formula for the chloride binding capacity of OPC pastes has been deduced. The new model is based on the chloride binding abilities of each hydrated phase, and therefore can distinguish between their contributions at different free chloride concentrations. When compared to experimental data, the results obtained using this new chloride binding isotherm have proven to accurately describe the chloride binding capacity of OPC pastes, results being within 12% of the experimental values for the whole range of free chloride concentrations considered, of up to 3 M.

Xiaohai Liu

Papers

Low carbon cementitious materials: Sodium sulfate activated ultra-fine slag/fly ash blends at ambient temperature

Effect of aluminum sulfate on the hydration of Portland cement, tricalcium silicate and tricalcium aluminate

Effect of triisopropanolamine on compressive strength and hydration of cement-fly ash paste

Effect of sodium sulfate and nano-SiO2 on hydration and microstructure of cementitious materials containing high volume fly ash under steam curing

Utilization of barium slag to improve chloride-binding ability of cement-based material