Publications

This study aimed at investigating the durability characteristics of the ambient-cured geopolymer concrete (GPC) developed using recycled coarse aggregate (RCA) and ultrafine slag (UFS). Two series of mixes were prepared. Natural aggregates (NAs) were replaced by RCA at different volume levels of 0, 25, 50 and 100% in both series. Meanwhile, UFS was added as a replacement by volume of fly ash at varying levels of 0, 15, and 30% in the first series, while UFS was used in addition to fly ash by percentage weight of fly ash at the levels of 0, 15, and 30% in the second series. The compressive strength, water absorption, chloride ion penetration, and carbonation depth of the developed ambient-cured GPC were studied. In addition, creep and drying shrinkage of the specimens were also examined. It was found that the compressive strength increased with the UFS content, while the opposite trend was observed with increasing RCA%. The highest compressive strength obtained with 100% RCA was 40.21 MPa (at 90 days), when 30% UFS was used in addition to fly ash. The addition of UFS not only helped in improving the strength characteristics but also provided an alternative to heat curing, which is a major drawback of GPC. Furthermore, the negative effects of RCA can also be minimised by adding UFS, which can be used as a compensator to RCA to improve the durability characteristics. The experimental results prove that susceptibility to chemical, water and chloride attacks can be mitigated by incorporation of UFS, and durable GPC can be produced by using RCA and UFS.

This paper proposes using neutral axis locations to monitor and quantify the prestress force in post-tensioned precast segmental beams. Strain measurements are used to obtain the neutral axis locations of specific cross-sections of the precast prestressed segmental beams, based on the plane–remains–plane and linear strain distribution assumption. A theoretical calculation method based on the static equilibrium of a specific cross-section is developed to calculate the prestress force in segmental beams based on the neutral axis location. To verify the accuracy of the proposed method, a post-tensioned prestressed segmental beam is built and tested in the laboratory. A corresponding high-fidelity finite element model is also developed based on the beam design and material properties. Experimental studies and numerical simulations are conducted to verify the feasibility and accuracy of the proposed method in quantifying the prestress force in precast segmental beams. Both experimental and numerical results demonstrate that the proposed method can reliably estimate the prestress force, which can be used to monitor the prestress force loss in post-tensioned structures.

This study proposes using glass fiber–reinforced polymer (GFRP) as a stay-in-place structural formwork for casting bridge decks with ultrahigh-performance concrete (UHPC). The GFRP stay-in-place formworks completely replace the bottom layer of rebars, and the top steel reinforcement is also replaced by a GFRP mesh to mitigate the corrosion damage. The formworks were either a flat GFRP plate with square hollow section (SHS) stiffeners or a flat GFRP plate with new Y-shape stiffeners. Concentric static tests on five 1:2.75 scale decks were performed to investigate the effect of stiffener's configuration and the influence of the concrete strength on the performance of bridge decks. Rotational fixity support was used to simulate a real bridge deck connection of supporting girders. All specimens with the stay-in-place formwork exhibited punching shear failure. It was found that the use of Y-shape stiffeners significantly improved the load-carrying capacity of the proposed deck. Replacing normal concrete with UHPC further improved the loading capacity of the deck. The decks demonstrated excellent performance, with the load-carrying capacity 3.8–9.5 times higher than the established equivalent service load depending on the concrete strength and configuration of the GFRP stay-in-place formwork. Deflection at service load was less than span/1,600 for all the decks. Compared with normal-strength concrete (34 MPa), UHPC improved the maximum load-carrying capacity of the deck from 91.4 to 149 kN.

Designing protective reinforced concrete (RC) beams against impact loadings is a challenging task. It requires a comprehensive understanding of the structural response of RC beams subjected to impact loads. Significant research efforts have been spent to unveil the impact response of RC beams by using analytical models, experimental testing, or numerical investigations. However, these studies used various assumptions in the analytical derivations and different test setups in the impact testing, which led to significantly different responses and observations of similar structures and similar loading conditions. For example, a minor change in contact surface can triple the maximum impact force of identical RC beams. This study provides a review of the contemporary understandings of the RC beam responses to impact loads, and explains the different observations and conclusions. Some unsolved issues for protective structures, that is, RC beams to resist impulsive loads are also discussed. It is suggested that future studies should take into consideration the conditions of the test setup, simplifications and assumptions made in analytical derivations for better interpretations of the obtained results.