It is well known that whether self-consolidating concrete (SCC) can be self-consolidated mainly depends on its flowability and segregation resistance. The shape and grading of coarse aggregate (CA) particles, as well as the arrangement of reinforcing bars, are two of the main factors influencing these properties. In this study, we developed a new meshless particle method that can reflect the influences of CA shape and rebar on concrete flow and segregation behavior during casting reinforced elements. Fresh concrete was represented by irregular CA particles and spherical mortar particles. CA particles were formed by small elementary particles (EP) to have their actual sizes and shape index. Then, the flow and segregation behaviors of two kinds of concrete in an L-shaped box with rebars were investigated experimentally and numerically, respectively. As a result, compared to the original double-phase & multi-particle (DPMP) method, the proposed numerical method improves the simulation accuracy by approximately 30% for flow behavior, and 20% for segregation behavior, respectively, during casting reinforced SCC using crushed stone as CA with poor shape, however, shows only a slight improvement when simulating the flow and segregation behaviors of SCC using artificial aggregate as CA with nearly spherical shape.

When concrete is subjected to the elevated temperatures of a fire, cracking occurs and the mechanical performance and durability deteriorate. Current crack repair methods using epoxy or polymer cement cannot repair microscopic damage and cannot restore the performances of whole concrete. There is no effective method to promote the recovery of concrete properties after fire. In this study, the authors proposed to use a highly permeable and alkaline silicate surface impregnation solution (NW-LS) to repair fire-damaged concrete, which is composed of sodium hydroxide (NaOH), lithium silicate (LS) and water and can penetrate in the inside of concrete. The concretes used in the experiments had the compressive strengths of 24.4 to 60.0 MPa before heating, and were heated at different temperatures (300, 500, 650°C) and then cooled in water or air. The changes in the performances, chemical compositions, and internal structure of the concretes after repairing were investigated in detail. The experimental results indicate that the repair densified the internal structure of heated concretes by the reaction between the silicate of the solution and the Ca(OH)₂ of the heated concretes, and greatly increased the compressive strength, carbonation resistance, and freezing-thawing resistance of the heated concretes. In addition, the alkalinity of heated concrete was restored by the NW-LS solution.

Tunnels that cross fault crush zones are subject to local deformation along these zones during earthquakes. Because the tunnel axis and the fault plane generally intersect in a three-dimensional manner, evaluating structural performance by using three-dimensional FEM is reasonable, and to this end selection of an appropriate damage indicator is required. To establish a damage evaluation method for the safety of tunnels subjected to local deformation, three-dimensional FEM analysis was carried out on previous loading experiments, the failure modes were analyzed, and the applicability of several damage evaluation indicators was verified. As a result, the damage to the tunnel in the model experiments was broadly classified into in-plane shear in the longitudinal section and out-of-plane shear in the longitudinal or transverse section. Performance evaluation using compressive damage indicators including minimum principal strain when the limit state of a tunnel is defined as the point at which the resistance to slippage in the crush zone is maximum was found to be feasible. Moreover, the results of the sensitivity analysis showed that evaluation based on the minimum principal strain is broadly applicable. Additionally, a limit value considering element size was proposed.

Unused residual concrete, retaining an excess water post-washing, is typically discharged at ready-mixed concrete plants, where it undergoes segregation into concrete debris and sludge. The significant expense incurred in managing concrete sludge disposal presents a pressing challenge. This study focuses on the high water absorbency of paper sludge ash (PSA) to develop a novel technology aimed at reducing excess water content in residual concrete. This is achieved by directly adding PSA into the drum of an agitator truck and agitating, thereby minimizing segregation. Laboratory experiments conducted with simulated residual concretes demonstrate that as the PSA-to-excess-water ratio increases, there is a corresponding reduction in slump value and amount of bleeding, coupled with an increase in compressive strength. Additionally, an equation is proposed for estimating excess water content in residual concrete using a time-domain-reflectometry, facilitating the calculation of PSA amount required on-site. The efficacy of the proposed equation is substantiated through demonstration experiments conducted at a ready-mixed concrete plant, affirming the significant property enhancement facilitated by PSA in residual concrete.