Influence of silica fume content on microstructure development and bond to steel fiber in ultra-high strength cement-based materials (UHSC)

Abstract

The use of silica fume can significantly enhance mechanical properties of concrete given its beneficial filling and pozzolanic effects. In this study, a simple and effective double-side pullout testing method was adopted to characterize the interfacial bond properties, which include pullout load-slip relationship, bond strength, and pullout energy, of steel fiber-matrix in ultra-high strength cement-based material (UHSC) with 0-25% silica fume by the mass of binder. The effects of silica fume content on flowability, heat of hydration, compressive and flexural strengths, hydration products, and pore structure of matrix at different curing time were evaluated as well. Backscatter scanning electron microscopy (BSEM) and micro-hardness measurement were used to examine the quality of interfacial transition zone (ITZ) around the fiber. In terms of the results, the optimal silica fume content could be in the range of 15%-25%. UHSC mixtures with these dosages of silica fume showed significant improvement in pullout behavior. Its bond strength and pullout energy at 28 d could increase by 170% and 250% compared to the reference samples without any silica fume. The microstructural observation verified the findings on the macro-properties development. Formation of more and higher strength of hydration products and refinement of ITZ around the fiber ensured higher micro-hardness, and thus increased the bond to fiber.

Revealing the dependence of the physiochemical and mechanical properties of cement composites on graphene oxide concentration

“…3,4 Recently, the use of nanoparticles in cementitious materials to improve their mechanical properties by controlling nanoscale crack formation has received widespread attention.…”

Intensified Pozzolanic Reaction on Kaolinite Clay-Based Mortar

“…The pore range of this peak (5-50 μm) is related to preexisting microcracks and entrained or entrapped air [45]. These pores, which did not change with curing ages, were possibly formed with the change of rheology of the mortar by SF addition [46]. As can be seen in Figure 6 that compares cumulative pore volumes of three samples at 28 days, the extra SF (over 7.5 wt %) is expected to play a role as a filler.…”

“…This indicates that the volume of mesopores (4.5-25 nm) of SF_15 were increased due to expansion with curing age. It has been reported that the pores finer than 10 nm mainly affect shrinkage and creep of hardened cementitious materials [46], and also the degree of capillary tension and stress for drying shrinkage is increased with a finer pore system (below 80 nm range in pore diameter) [15,48]. Thus, this distinct expansion might be attributed to the accelerated drying shrinkage of matrix and resultant micro cracks, as shown in the low W/B (0.25) cement paste with SF (20% of cement) [49].…”

“…The pore range of this peak (5-50 µm) is related to preexisting microcracks and entrained or entrapped air [45]. These pores, which did not change with curing ages, were possibly formed with the change of rheology of the mortar by SF addition [46]. The measured pore volume was divided into four size ranges in Figure 7, on the basis of the international union of pure and applied chemistry system [45].…”

Fracture toughness and failure mechanism of high performance concrete incorporating carbon nanotubes

“…The studies show that these inclusions not only improve the packing of particles but also produce crack bridging phenomena by densifying the nanostructures [18,27]. Nano particles control the C-S-H reaction and improves the concrete durability [28][29][30][31][32][33]. Among above mentioned nano materials, MWCNTs possess unique and exceptional characteristics in terms of physical and mechanical properties.…”