To investigate the effect of reinforcement corrosion on the bond properties between concrete and reinforcing steel bar, pullout tests were conducted on a total of 20 specimens using corroded reinforcement bars embedded in concrete specimens. No. 3 (9.5-mm diameter) and No. 6 (19-mm diameter) bars corroded by an accelerated corrosion method were selected for testing. Two groups of corrosion specimens were prepared: one was whole-surface corroded (100%), and the other was partial-surface corroded with 40, 60, and 100% corrosion. Each group of specimens included four levels of corrosion: 3, 5, 10, and 15%. Results indicate that the tensile strength of steel bar decreases with the increase of corrosion level. Corrosion levels less than 3% present a minor tensile-strength reduction of approximately 3%, whereas the tensile strength may decrease to 75–90% when the corrosion level increases more than 10%. The critical bond strength and ultimate bond strength of corroded bars may increase slightly with cor...

To investigate potential implications of microbial activity on sand bioconsolidation and subsurface environments, two ureolytic strains, Sporosarcina pasteurii and Bacillus subtilis were tested for the production of calcium carbonate (CaCO₃). Laboratory experiments with monoculture S. pasteurii (column 1) and coculture S. pasteurii-B. subtilis (column 2) were conducted to determine urea and calcium chloride reactivity and volumetric carbonate formation. Both columns were able to consolidate sand, whereas, column 1 induced greater CaCO₃ precipitation. X-ray diffraction (XRD) and scanning electron microscopy (SEM) showed two columns with different mineralogy with calcite, and vaterite formation. Column 1 showed rhombohedral and trigonal crystals morphology, whereas column 2 developed the prismatic calcite and the spherulite vaterite crystals might be due to the differences of the micro-environment caused by the urease expression of these bacterial species. These results indicate the possibility of using those crystals to cement loose sand whereas, highlighted the importance of combining these techniques to understand the geomicrobiology found in the subsurface environments.

This study focuses on evaluating the effects of the fineness of fly ash on the strength, fracture toughness, and fracture resistance of concrete. Three fineness levels of fly ash that respectively pass sieves—no. 175, no. 250, and no. 32—were used. In addition to the control concrete mixture without fly ash, two fly ash replacement levels of 10% and 20% by weight of the cementitious material were selected for the concrete mixture. The experimental results indicate that the compressive strength of the fly ash concrete decreases with the increase in the replacement ratio of fly ash but increases in conjunction with the fineness level of fly ash. The presence of finer fly ash can have beneficial effects on the fracture energy (G_F) of concrete at an early age (14 days) and attain a higher increment of G_F at a later age (56 days). The concrete containing finer fly ash was found to present larger critical stress intensity factors (K^S_IC) at various ages, and the K^S_IC also increases in conjunction with the fineness levels of fly ash.

This research aimed to investigate the engineering and dynamic properties, such as unit weight, stiffness, natural frequency and damping ratio, of lightweight aggregate concrete (LWAC) beams made with sedimentary lightweight aggregate (LWA) and to compare with companion normal weight concrete (NWC) beams. The primary design variables included compressive strengths of 20, 40, and 60 MPa and reinforcement ratios of 0%, 1.03%, and 2.32%, respectively. A total of 62 beams were made and tested. Test results showed that the unit weight of LWAC beams was about 16–23% lower than that of NWC beams for the same strength level. In addition, the reduced modulus of elasticity of LWAC resulted in a stiffness decrease of reinforced lightweight concrete (RLC) beams of 5–15% related to the reinforced NWC (RC) beams. Nevertheless, the natural frequency of RLC was still higher by about 1–10% than that of RC. In contrast, it was also found that the porous LWA with high damping capacity enhanced the damping ratio of RLC beams...

Self-consolidating lightweight aggregate concrete (SCLC) is a highly flowable and lightweight concrete. In this study, the properties of SCLC and prestressed SCLC members were tested and compared with those made of normal-weight self-consolidating concrete (SCC). The test results show that SCLC can be used for prestressed concrete members. The use of lightweight aggregates with a particle density larger than 1100 kg/m³ can avoid the serious segregation of fresh concrete. In addition, the SCLC designed in this study can meet most of the SCC Rank 2 test standards, except for the V-funnel test. The water contained in the lightweight aggregates supplied sustained curing, so the level of drying shrinkage of the SCLC was lower than that of the conventional SCC. However, the level of creep of the SCLC was higher than that of the conventional SCC, because normal-weight aggregates are more able to inhibit the change of the concrete’s volume. On-site test results show that after 180 days of prestressing, the prestress loss was about 5.35–6.83% for the full-size SCLC members, which was smaller than that for the conventional SCC members (about 8.19–9.06% loss).

The effects of particle size of ground granulated blast furnace slag (GGBS) on the fracture energy, critical stress intensity, and strength of concrete are experimentally studied. Three fineness levels of GGBS of 4000, 5000, 6000 cm²/g were used. In addition to the control mixture without slag, two slag replacement levels of 20% and 40% by weight of the cementitious material were selected for preparing the concrete mixtures. The control mixture was designed to have a target compressive strength at 28 days of 62 MPa, while the water to cementitious material ratio was selected as 0.35 for all mixtures. Test results indicate that using finer slag in concrete may improve the filling effect and the reactivity of slag, resulting in a larger strength enhancement. The compressive strength of slag concrete was found to increase in conjunction with the fineness level of the slag presented in the mixture. Use of finer slag presents a beneficial effect on the fracture energy (G_F) of concrete, even at an early age, and attains a higher increment of G_F at later age (56 days). This implicates that the finer slag can have a unique effect on the enhancement of the fracture resistance of concrete. The test results of the critical stress intensity factor (K^S_IC) of the slag concretes have a similar tendency as that of the fracture energy, indicating that the finer slag may present an increase in the fracture toughness of concrete.