International Concrete Abstracts Portal

A conceptual design screening workflow for reinforced concrete (RC) columns is presented to conjointly minimize raw-material cost and cradle-to-gate carbon footprint prior to reinforcement detailing. The method proposes modifications to ACI 318-19 sizing procedures to incorporate performance-based cost and environmental metrics before reinforcement detailing, thereby enabling rapid screening of candidate concrete mixtures, reinforcement ratios, and column configurations. The workflow is demonstrated on a 12-story building using 30 concrete formulations, four reinforcement ratios, three cross-sectional shapes, and two steel rebar production routes. Results show that: 1) decreasing reinforcing-steel content and the embodied carbon footprint of materials on a per-unit-volume basis does not necessarily minimize the total carbon footprint of RC columns; 2) steel reinforcement can contribute up to three times more embodied carbon than concrete; and 3) eco-efficiency exhibits a weak correlation with binder content and concrete type.

This study developed an interpretable machine learning (ML) framework to predict the thermal conductivity of fiber-reinforced mortars (FRMs). Traditionally, thermal conductivity is determined using experimental methods that are material-, time-, and cost-intensive, motivating the development of ML prediction models. Extreme Gradient Boosting (XGB), Random Forest (RF), Artificial Neural Networks (ANN), and Support Vector Machines (SVM) were evaluated as ML models. Missing data were addressed using Multiple Imputation by Chained Equations (MICE), K-Nearest Neighbors (KNN), and Singular Value Decomposition (SVD). The XGB model with SVD imputation achieved the best performance, with a test accuracy of 86%, which improved to 90% after feature selection and hyperparameter tuning. Model interpretation identified fiber diameter, fiber content, and sand proportion as key influencing factors. Experimental validation showed reliable predictions, with accuracy up to 97% for mid-range conductivity values. The proposed framework provides a practical tool for predicting the thermal conductivity of cementitious materials.

Infilled cementitious composite (ICC) is produced by infilling cementitious paste into a designed aggregate skeleton. This approach enables the incorporation of both coarse aggregate and fibers while maintaining adequate fresh and hardened performance at minimal paste volume. In this study, ultra-high-performance concrete (UHPC) pastes incorporating supplementary cementitious materials were infilled into fiber-aggregate skeletons (FAS) with macro steel fiber volumes ranging from 0 to 2.0%, yielding a total of 16 ICC mixtures. The FAS packing density, UHPC infilling ability, and the fresh, mechanical, and microstructural properties of both UHPC paste and the resulting ICC were evaluated. The 28-day compressive strength of ICC ranged from 96.0 (13.9 ksi) to 121.6 MPa (17.6 ksi), while the first-cracking flexural strength increased by up to 61.8% at a fiber volume of 2.0%. The cement content of ICC ranged from 229 to 1116 kg/m3 (14.3 to 69.7 lb/ft3). Relative to the corresponding conventional UHPFRC without coarse aggregate, ICC reduced material cost by up to 50% and embodied CO2 by up to 55%. These findings demonstrate that ICC can provide a low-carbon, material-efficient pathway for sustainable structural concrete.

This study evaluates semi-refined (SR-) kappa (κ)-carrageenan extracted from Kappaphycus alvarezii as a viscosity-modifying admixture (VMA) for cement pastes (water-cement ratio [w/c] = 0.43). Extraction parameters, potassium hydroxide (KOH) concentration (6 to 12%), temperature (104 to 176°F [40 to 80°C]), and residence time (1 to 3 hours) were varied, and the resulting materials were assessed for modified Bingham rheology (yield stress and plastic viscosity​), viscoelastic properties (storage modulus and critical shear strain), structural build-up kinetics (build-up index), forced bleeding, hydration induction period, and early compressive strength. SR-(κ)-carrageenan produced under a low-severity operating point (6% KOH, 104°F [40°C], 1 hour) and dosed at 4% (by mass of water) increased yield stress​ from 0.21 to 0.42 lb/ft2(10 to 20 Pa) and plastic viscosity​ from 0.42 to 0.80 lb/ft–s (0.63 to 1.18 Pa∙s). It enhanced early-age rigidity and build-up from 9.29 to 22.03 lb/ft2∙s–3/2 (445 to 1055 Pa/s3/2) and reduced forced bleeding relative to the reference. The induction period increased moderately (from 1.4 to 2 hours), and no early-age strength penalty was observed at 1 and 7 days. Compared with pure R-(κ)-carrageenan, SR-(κ)-carrageenan maintained (κ)-carrageenan rheology and structural build-up kinetics while producing a smaller induction-time shift in this paste class. Within the tested matrix, dosages, and protocols, the test results support SR-(κ)-carrageenan as a cement-grade VMA candidate produced through processed Eucheuma seaweed/alkali-treated cottonii (PES/ATC)-aligned unit operations.

The alkali-silica reaction (ASR) in seawater-sea-sand cement-based materials (SWSSCM) applied in marine engineering cannot be underestimated because seawater and sea sand have a high content of alkali ions. To reduce the ASR in SWSSCM, this paper compares the inhibition effects of three kinds of supplementary cementitious materials (SCMs). The results show that the expansion rate of SWSSCM without SCMs is up to 0.212% at 14 days, which shows high ASR risk. The incorporation of SCMs can efficiently reduce the ASR risk in SWSSCM. Compared with that of SWSSCM without SCMs, the expansion rate of SWSSCM with 50% metakaolin, fly ash, and slag at 28 days can be reduced by 94.8%, 90.7%, and 80.6%, respectively; the content of crystalline ASR product Na-shlykovite (NaCaSi4O8(OH)3·2.3H2O) is decreased by 81.4%, 69.2%, and 47.9%, respectively; and the content of less-harmful pores is increased by 76.8%, 48.1%, and 36.9%, respectively. The inhibition effects of metakaolin and fly ash on ASR are better than that of slag, and the suggested optimal contents of metakaolin, fly ash, and slag to replace cement are approximately 10 to 20%, 20 to 30%, and 30 to 40%, respectively. Moreover, the physical and chemical inhibition effects of SCMs on the ASR in SWSSCM are clarified, which provides the basis for the durability design of SWSSCM in the marine environment.