The influence of expansive cement on the mechanical, physical, and microstructural properties of hybrid-fiber-reinforced concrete

Abstract

This work reports the properties of hybrid-fiber-reinforced concrete (HyFRC) made with expansive (Type K) cement. Combinations of metallic and non-metallic fibers at total fiber volume fraction of 1% were studied. The effectiveness of double hooked-end (DHE) steel fibers in concrete containing expansive cement is investigated for the first time in this study. The mechanical, physical, and microstructural properties of concretes have been assessed. Additionally, the fiber pull-out test was also performed to investigate the effectiveness of Type K cement in improving the fiber-matrix interfacial bond. The results indicate that Type K cement has small in-fluence on the mechanical properties of concrete fabricated at the same water-cement ratio of 0.35 with a similar consistency. However, as expected, it enhances the volume stability of concrete subjected to drying condition. The pull-out resistance of steel fibers increased by 26% as a result of full replacement of ordinary Portland cement (OPC) with Type K cement. A deflection-hardening performance is achieved by introducing of DHE steel fibers in HyFRC. The partially replacement of DHE steel fibers with other type of fibers results in a reduction in the strengths of HyFRC. The results obtained in this study proves that the bond between fiber and cement matrix is enhanced by fully replacement of OPC with expansive cement, which subsequently improves the mechanical properties of HyFRC.

Shrinkage and Mechanical Properties of Self-Compacting SFRC With Calcium-Sulfoaluminate Expansive Agent

“…Therefore, with the increase of the v f from 0.4% to 1.2%, the expansion rate of self-compacting SFRC reduced 58.2% at the early 3 d, and the expansive time of SF12 was shorted as about half of SF4. Similar results were reported in literatures [28][29][30]. This led to the higher autogenous shrinkage before 90 d, and the autogenous shrinkage at 28 d of SF12 was about twice that of SF4.…”

“…This may be attributed to the self-prestress effect. The cementitious matrix expansion confined by steel fibers leads a reciprocal interfacial stress between fibers and matrix, which induces an internal uniform compressive prestress of matrix, and improves the chemical bond between steel fibers and cementitious matrix [30,46]. By using Equation (3) in China code JGT 472 [42], the tested values (f t ) and calculated values (f t,c ) are compared in Table 8.…”

“…Therefore, the presence of steel fibers in SCC could confine the expansion [28,29], the expansion rate abated 81.5% of self-compacting SFRC with steel fiber (circular section, l f = 35 mm, d f = 0.55 mm) of v f = 0.75% compared to that of SCC under the standard curing condition at (20 ± 2) • C temperature and RH ≥ 95%, while a slight decrease of the expansion rate at about 0.07% of self-compacting SFRC with the v f = 0.25-0.75% was produced under the sealed cure and top-surface exposure curing conditions. uAfroughsabet et al [30] presented that the conventional SFRC with K-type expansive cement was improved by 28.4% of cylindrical compressive strength and 39.2% of splitting tensile strength with the v f = 1.0% hooked-end steel fibers, while the expansion was fully cancelled due to the inhibition effect of fibers. Geng et al [31] also reported that to ensure the workability of a fresh mixture by increasing 7% binder and reducing 8.8% coarse-aggregate, the drying shrinkage of conventional SFRC with the v f = 0.8% increased by 22.2%, which could not be removed by adding expansive agent.…”

Evaluation of Engineering Properties of Calcium Sulfoaluminate Cement-based Concretes Reinforced with Different Types of Fibers

“…Therefore, the influence of PVA fibers on the splitting tensile strength is not comparable to that of the steel fibers. Furthermore, DHE steel fibers utilized in the current study created remarkably increased pullout forces with respect to other fibers due to the anchoring mechanism, which led to an improved tensile strength [26]. Noushini et al [45] also investigated the influence of PVA fibers with different lengths and at various fiber contents.…”

“…Additionally, the shrinkage of concrete can cause cracking in early stages and subsequently shortening of the serviceability of the concrete structure as a result of exposure to harmful substances [22]. The introduction of discrete fibers is accepted as a favorable solution in the manufacturing of composites with increased mechanical characteristics, because it controls the propagation of cracks [23,24,25,26,27]. Moreover, fibers can decrease drying shrinkage deformation either by improving cohesion between the concrete matrix and fibers, which contributes to physically restraining shrinkage [28], or controlling cracks (the most important effect of fibers in the shrinkage of concrete [29]).…”