International Concrete Abstracts Portal

The reduction in shear capacity when using recycled coarse aggregate (RCA) made from crushed concrete is evaluated in terms of tensile cracking and fracture-surface characteristics. An experimental investigation into the fracture and flexure-shear behaviors of recycled aggregate concrete (RAC) is presented. Replacing natural aggregate in concrete proportioned for 30 MPa (4350 psi) compressive strength with RCA results in lower compressive and tensile strengths. The tensile fracture-surface characteristics vary between RAC and natural aggregate concrete (NAC). While the surface area created in the tensile fracture of RAC is larger than that of NAC, the fracture surface profile in RAC has a smaller roughness than NAC. In the flexure-shear response of reinforced concrete beams, the dilatancy determined from the slip and crack opening displacements measured across the shear crack is smaller in RAC than in NAC. The failure in the reinforced beam is due to the frictional stress transfer loss across the primary shear crack. There is a larger decrease in the shear capacity with the use of RAC than indicated by the reduction in compressive strength. The reduced shear capacity of reinforced RAC is due to the combined influences of reduced tensile strength and crack surface roughness. The design provisions require calibration for crack surface roughness when using RAC in structural applications.

The use of parametric/natural fires in the design of reinforced concrete structures in fire conditions requires an accurate definition of the temperature-induced evolution of the thermal and mechanical properties. Within this context, the characterization of four normal-strength concretes (f_c²⁰ = 4220-7000 psi [29-47 MPa]), with siliceous and carbonate aggregates are studied here as concerns the thermal diffusivity D (between 68 and 1644°F [20 and 900°C]) and under uniaxial compression after different thermal cycles, with reference maximum temperatures of 392, 752, and 1112°F [200, 400, and 600°C]. The results show that thermal diffusivity exhibits mostly irreversible behavior after exposure to temperatures over 1382°F [750°C]. As concerns the compressive strength, the hot and residual values (when TT_test = 68°F [20°C]) are, overall, in line with the most common standard provisions. Quite interestingly, the tests carried out at intermediate temperatures (with T_test does not = T_max and T_test > 68°F [20°C]) highlighted a strength decay, which is not simply an interpolation between hot and residual values.

ASTM C31 describes the procedure for making concrete specimens in the field. Its origin can be traced to 1920, proposing rodding or stroking each 100 mm thick layer 25-30 times. Concrete technology has evolved tremendously over the last century, but specimens are still prepared following this 100-year-old methodology. This paper investigates the density and compressive strength of concrete cylinders for different consolidation procedures. Mix design variations include paste volume, w/c, aggregate grain size distribution, fly ash, and plasticizer. An increase in compressive strength of approximately 5 MPa can be obtained if 100 × 200 mm cylinders are rodded in 4 layers, 25 rods each, if the slump is not over 100 mm. For all other mixtures, the current rodding procedure of 2 layers, 25 rods each, is recommended. For mixtures with higher slump, 2 layers with less rodding per layer deliver similar strength values, but the variability is high.

This paper proposes new procedures for determining allowable loads for power-actuated fasteners that are consistent with ASCE/SEI 7-22. Thirty new load test datasets for single fasteners in shear and tension, and fastener groups in shear, are analysed statistically. The current ICC-ES AC70-2021 procedure yields allowable loads that are quite variable, even negative, and very sensitive to “reject-as-outlier” decisions. In addition, ICC-ES AC70-2021 procedures to determine allowable loads can currently not be clearly linked to the reliability requirements per ASCE/SEI 7-22. Monte Carlo simulation demonstrates that the proposed Simplified Method, derived from the described Detailed Method, is robust for sample sizes as small as ten specimens. It yields Allowable Fastener Loads that are 10 to 25% greater than those obtained using the current ICC-ES AC70-2021 procedure, yet are typically 60 to 90% of the actual Allowable Fastener Loads, derived from the described Detailed Method to assess allowable loads in line with ASCE 7 reliability requirements. The new provisions are extended to cases where the coarse aggregate hardness in the test specimens differs from that in the structure, which is not addressed in ICC-ES AC70.

This study investigated the flexural behavior and seismic connection performance of precast lightweight aggregate concrete shear walls (PLCWs) using the relative emulation evaluation procedure specified in the Architectural Institute of Japan (AIJ). Six PLCW specimens connected through a bolting technique were prepared and tested under constant axial and cyclic lateral loads. In addition, three companion shear walls connected through the most commonly used spliced sleeve technique for precast concrete members were prepared to confirm the effectiveness of the bolting technique for the seismic connection performance. The main parameters were the concrete type (all-lightweight aggregate (ALWAC), sand-lightweight aggregate (SLWAC), and normal-weight concrete (NWC), the compressive strength of the concrete, and the connection technique. The test results showed that none of the specimens connected through the conventional spliced sleeve technique reached the allowable design drift ratio specified by the AIJ, indicating that the spliced sleeve is an unfavorable technique for obtaining a seismic connection performance of PLCWs equivalent to that of cast-in-place reinforced concrete shear walls. However, the specimens made of ALWAC or NWC and connected through the bolting technique not only reached the allowable design drift ratio specified by the AIJ but also satisfied the requirements of the seismic connection performance (lateral loads and allowable error at yield displacement) within the allowable design drift ratio. Consequently, the displacement ductility ratio of the specimens connected through the bolting technique was 1.52 times higher than that of the specimens connected through the conventional spliced sleeve technique, respectively. This difference was more prominent in the specimens made of ALWAC than in those made of SLWAC or NWC. Thus, the use of the bolting technique as a wall-to-base connection in shear walls can effectively achieve a seismic connection performance equivalent to that of cast-in-place shear walls while maintaining the medium ductility grades.