International Concrete Abstracts Portal

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.

As global demand for concrete has been forecasted to keep rising, one of the approaches towards more sustainable constructions is the adoption of mix designs replacing conventional ones. The current study contains a comparison between concrete mixes that constitutes only Ordinary Portland Cement (OPC) and mixes incorporating 25% OPC with a 75% replacement by supplementary cementitious materials (SCM). The major experimental hypothesis circles around investigating whether it is effective to use thermal treatment under moderately elevated temperatures to enhance the physical and mechanical properties of concrete. Comparisons were performed using mechanical tests such as: compressive strength, tensile strength, flexural strength, and through several non-destructive physical experiments as well as microstructural investigation using SEM and EDS. In conclusion, the experimental results have shown a mostly positive influence observing significant enhancements after thermal treatment. However, treated concrete mixes that constitute only OPC seem to excel in overall performance compared to those incorporating SCM.

Despite the advantageous features of earthen construction for sustainability, certain limitations arise, notably the time-intensive nature of the construction process. Some efforts have been made to achieve self-consolidating earth concrete (SCEC) by overcoming the presence of fine particles to achieve adequate rheology. The impact of cement, metakaolin, and limestone filler on dry flowability characteristics, rheology, workability, and compressive strength of self-consolidating earth paste (SCEP) mixtures was assessed in this study. The investigated mixtures were proportioned with different clay compositions, polycarboxylate ether (PCE), with/without the initial addition of sodium hexametaphosphate (NaHMP) as a clay dispersant. It was revealed that the addition of NaHMP and metakaolin to the mixtures consisting of finer clay particles significantly increased static yield stress, build-up index, critical shear strain, and storage modulus evolution. Finally, the contribution of dry flowability characteristics of the powders to the rheological properties of the SCEP mixtures was investigated to facilitate the selection process.

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.

The term “mass concrete” characterizes a specific concrete condition that typically requires unique considerations to mitigate extreme temperature effects on a structure. Mass concrete has historically been defined by the physical dimensions of a massive concrete element with the intent of identifying when differential temperatures may induce early-onset cracking, leading to reduced service life. More recently, in addition to differential temperature considerations, extreme upper temperature limits have been imposed by the American Concrete Institute to prevent long-term concrete degradation. Studies dating back to 2007 show shafts as small as 48 in. (1.2 m) in diameter can exceed both differential and peak temperature limits; in 2020, augered cast-in-place piles as small as 30 in. (0.76 m) in diameter exceeded one or both limits. This suggests the term “mass concrete” is misleading when considering today’s high-early-strength or high-performance mix designs. This study applies numerical modeling coupled with field measurements to investigate the effects of concrete mix design, drilled shaft diameter, and environmental conditions on heat energy production and temperature. Further, the outcome of this study focuses on developing criteria that combine the effects of both size and cementitious material content to determine whether unsafe temperature conditions may arise for a given drilled shaft design.