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Open research questions in Concrete and Cement Materials Research

62 unresolved questions extracted from the limitations and future-work sections of 1,249 Concrete and Cement Materials Research papers in our library. Each links back to the study that raised it.

What the literature leaves open

  • Abstract Graphene nanoplatelets (GnPs) have shown promise in enhancing cementitious materials, yet their interaction with calcium-silicate-hydrate (C-S-H), the primary cement binding phase, remains insufficiently understood.

    Graphene Nanoplatelet–Driven Structural Modifications in Synthetic Calcium-Silicate-Hydrate · 2026 · DOI

  • Although granite (GN) and dolomite (DM) wastes are abundant by-products, their use in AAS materials for performance enhancement has not been systematically investigated.

    Complementary Activation Mechanisms of Granite and Dolomite Wastes in Optimizing Alkali-activated Slag Composites · 2026 · DOI

  • 1. Future studies are recommended to investigate the Aloe vera-GGBS-cement hybrid stabilizing agent on a wider range of soil types and classifications. It is recommended that the mixture be tested on soils with varying initial California Bearing Ratio (CBR) values. 2. 3. Further research may investigate a broader range of mix proportions to determine the most optimum mix design.

    Formulation and Evaluation of an Aloe Vera–Based Hybrid Soil Stabilizing Agent Incorporating GGBS and Cement for Base Course Improvement · 2026 · DOI

  • Summary This study evaluated an Aloe vera-based hybrid soil stabilizing agent combined with GGBS and cement to enhance base course bearing capacity using an experimental design. Sieve analysis of the untreated soil (T0) revealed a well-graded distribution matching DPWH Item 204 Grading B, while its Liquid Limit (20.99%), Plastic Limit (13.56%), and Plasticity Index (7.43%) classified it as A-2- 4(0). Duplicate samples for mixtures T1, T2, and T3 were prepared using Relative Percent Difference (RPD) to ensure precision. Compaction testing (ASTM D698) showed the stabilizer effectively reduced the Optimum Moisture Content (OMC) and increased the Maximum Dry Density (MDD) across all treated groups, achieving higher dry density with less moisture. Performance evaluation after 7-day curing revealed untreated soil averaged a low 36.23% soaked CBR, failing the 80% DPWH requirement for untreated base course. Following treatment, T1 averaged 85.13% CBR, failing the 100% DPWH Item 204 threshold for treated materials, whereas T2 and T3 significantly surpassed it at 147.10% and 205.05%. One-way ANOVA and Tukey's HSD analysis confirmed statistically significant differences in CBR values among groups. The analysis for T3 revealed a key synergistic effect where the bio-polymer acted as a catalyst, retaining the sustained moisture required for the pozzolanic hydration of GGBS. Field Density Tests verified 100% relative compaction compliance, replicating laboratory MDD. Lastly, mixture T2 was determined to be the most economical and practical choice, balancing performance, sustainability, and constructability while providing a substantial margin above the standard.

    Formulation and Evaluation of an Aloe Vera–Based Hybrid Soil Stabilizing Agent Incorporating GGBS and Cement for Base Course Improvement · 2026 · DOI

  • While the study provides valuable insights into the use of RHA in pavement applications, several methodological and scope-related limitations should be carefully considered. First, this study adopts a cradle-to-laid LCA approach, which, while consistent with established practices for pave- ment analysis, limits the comprehensiveness of the environ- mental evaluation compared to a complete cradle-to-grave LCA. By focusing solely on processes from raw material extraction through pavement placement, this analysis over- looks important downstream stages, such as maintenance activities and end-of-life management, which can signifi- cantly affect long-term sustainability outcomes. Second, the Ec, a key parameter for evaluating mechani- cal performance, was not directly measured; instead, it was estimated using empirical correlations based on compres- sive strength, which may introduce uncertainty into the structural assessment. This approach was adopted due to experimental constraints and the primary focus of the study on strength-related properties rather than full mechanical characterization. Regardless, the use of these formulations may lead to overestimation or underestimation of stiffness, as such relationships do not explicitly account for variations in microstructure, porosity, or the presence of SCMs. Con- sequently, PCC mixtures with similar compressive strength but different internal structures may exhibit significantly different elastic responses, introducing systematic bias in the estimated values. Irrespective of this, widely accepted design codes and standards worldwide commonly employ such correlations, as they provide a practical and sufficiently reliable approximation of elastic behaviour for comparative assessment. Page 19 of 26 359 Third, although the use of the AASHTO-93 method is appropriate for preliminary pavement design [77, 101, 102], the absence of experimentally determined strain–stress rela- tionships and fatigue properties of the asphalt mixtures, together with the lack of direct measurements of the sub- grade’s resilient modulus, constitutes a significant limitation. These parameters are fundamental inputs for both empirical calibration and mechanistic–empirical refinement, and their omission may affect the reliability and representativeness of the predicted structural performance. In particular, the use of literature-based values may not adequately capture site- specific conditions, potentially leading to deviations in layer thickness design and service life estimation. Consequently, the results from this research should be interpreted as indic- ative rather than definitive, and future work should incorpo- rate dedicated laboratory and in-situ testing to enable a more rigorous mechanistic–empirical validation of the proposed pavement structures. Fourth, from an environmental perspective, the LCI did not include reinforcing steel components (i.e., dowel bars and tie bars). This exclusion is justified by the minimal amount of steel required across scenarios, their weak cor- relation with RHA content, and the high variability in their application, which depends on construction practices rather than the design of the composite materials. Consequently, while the outcomes of this research provide meaningful insights into the technical and envi- ronmental feasibility of incorporating RHA, future work incorporating additional direct mechanical measurements and broader inventory data would enhance the robustness and applicability of the findings obtained herein.

    A Colombian case study in Rice Husk Ash (RHA)-modified Portland cement concrete: integrating mechanical performance, pavement design, and life-cycle assessment · 2026 · DOI

  • Moreover, the combined use of Raviz pozzolan with other SCMs (such as fly ash or microsilica) should be explored to identify pos- sible synergistic effects on ASR mitigation and overall con- crete performance. Other perfor- mance aspects, such as compressive strength, permeability, 1 3Innovative Infrastructure Solutions (2026) 11:363 363 Page 8 of 9 and long-term durability under field exposure, were not investigated.

    Determining the optimum percentage of natural pozzolan to reduce the alkali–silica reaction in concrete · 2026 · DOI

  • recommendation The results of this study indicated that Site Curing 2 (SC2) is better than Site Curing 1 (SC1) in terms of volume of per- meable voids, compressive strength, water absorption, and sorptivity test. It did not consider factors such as carbon- ation depth, chloride ion penetration, sulphate resistance, and microstructural analyses such as SEM, XRD, or MIP. Only two curing condition regimes were used, and other sustainable curing methods, such as internal curing, mem- brane curing, or the use of curing agents, were not consid- ered. Further studies should focus on long-term field trials to confirm laboratory results. In actual building settings, multi- scale studies with mechanical, durability, and microstruc- tural characterization. In addition, more accurately correlate the evolution of pore structure with long-term performance, and explore new curing technologies that may offer solu- tions to improve concrete durability while reducing water and labor use. Funding The authors for this research received no funding specific grant from any funding agency, etc. Data availability The (figure/table) data used to support the findings of this study are included within the article.

    Evaluation of surface and durability characteristics of ready-mixed concrete under various curing conditions · 2026 · DOI

  • While a detailed life-cycle assessment is beyond the scope of this work, these preliminary considerations highlight that OHA not only improves engineering properties but also offers broader environmental, economic, and societal bene- fits, reinforcing its potential as a sustainable construc- tion material.

    Performance evaluation of concrete incorporating oat husk ash from cold regions as a supplementary cementitious material · 2026 · DOI

  • The investigation was conducted under controlled laboratory conditions, and long-term exposure behavior was not studied. The mechanical performance of the concrete mixes was evaluated using the results of compressive, split tensile, and flexural strength tests. The durability aggressive environments. The microstructural characterization was primarily based on FESEM-EDAX observations. Advanced techniques, such as MIP, could provide deeper into hydration and pore structure. assessment was focused on selected insight FIGURE 23 The compressive strength, cost, and CO2 emissions of the HPC mixes. enhances the eco-efficiency of the concrete by achieving higher strength and durability with lower cement consumption.

    Synergistic densification strategy for sustainable high-performance concrete: a ternary binder packing framework · 2026 · DOI

  • Compaction-related parameters (MDD and OMC) show relatively lower SHAP values (±5 range) and secondary effectiveness compared to chemical bonding processes, but the minimum compaction threshold required before chemical stabilization becomes effective in fly ash and WPS-stabilized soils has not been quantified.

    Prediction of unconfined compressive strength of fly ash and waste paper sludge stabilized clayey soil using explainable machine learning · 2026 · DOI

  • The stacking ensemble model demonstrates superior performance over individual Random Forest and XGBoost models for predicting UCS, but the paper does not investigate how model generalization transfers to different soil types, clay mineralogy compositions, or geographic regions beyond the dataset studied.

    Prediction of unconfined compressive strength of fly ash and waste paper sludge stabilized clayey soil using explainable machine learning · 2026 · DOI

  • The indirect and interaction-driven role of WPS in stabilization is identified through SHAP values concentrated around ±35, indicating minimal direct contribution, but the optimal WPS dosage and its synergistic effects with fly ash at varying curing periods have not been systematically characterized through sensitivity analysis.

    Prediction of unconfined compressive strength of fly ash and waste paper sludge stabilized clayey soil using explainable machine learning · 2026 · DOI

  • The strong multicollinearity observed between soil properties (LL, PL, DFS with r > 0.94) justifies the use of ensemble machine learning over traditional regression, but the paper does not compare the relative performance gains of ensemble methods versus dimensionality reduction techniques (PCA, feature selection) for this specific fly ash and waste paper sludge stabilization problem.

    Prediction of unconfined compressive strength of fly ash and waste paper sludge stabilized clayey soil using explainable machine learning · 2026 · DOI

  • Random Forest models demonstrate sensitivity to extreme values in higher unconfined compressive strength ranges with residuals up to ±10 kPa, but the paper does not investigate why this limitation occurs or propose methods to improve prediction accuracy specifically for high-strength stabilized soil samples beyond the dataset range studied.

    Prediction of unconfined compressive strength of fly ash and waste paper sludge stabilized clayey soil using explainable machine learning · 2026 · DOI

  • The SHAP-based feature importance analysis reveals that WPS (waste paper sludge) acts primarily through physical modification rather than direct chemical contribution, but the interaction mechanisms between WPS and fly ash during stabilization have not been experimentally validated. The paper recommends validation through experimental or field studies to establish direct causal relationships beyond the data-driven model predictions.

    Prediction of unconfined compressive strength of fly ash and waste paper sludge stabilized clayey soil using explainable machine learning · 2026 · DOI

  • While the optimum stabilizer content was determined at 4%, the mechanism of why excess chemical (beyond 4%) reduces CBR values is not fully explained.

    Stabilization of Expansive Clay Using Calcium Lignosulfonate for Subgrade Application · 2026 · DOI

  • The porosity and point load test correlation is weak for dolomite (R² = 0.42) compared to limestone (R² = 0.84), suggesting the need for further investigation into the mechanisms governing this relationship.

    Influence of Petrographic Properties on the Strength and Durability of Dolomite and Limestone for Infrastructure Development · 2026 · DOI

  • The environmental assessment focused only on the material production stage within a cradle-to-gate scope. Given the enhanced freeze-thaw durability observed, potential reductions in maintenance frequency and associated environmental impacts during the service period may be expected; however, these effects were not quantified.

    Comprehensive evaluation of the environmental performance and durability of biochar-incorporated concrete · 2026 · DOI

  • Future studies are recommended to include quantitative evaluation of ITZ thickness and elemental distribution using EDS-based compositional analysis in blended cementitious systems.

    Comprehensive evaluation of the environmental performance and durability of biochar-incorporated concrete · 2026 · DOI

  • In addition, the effects of ultrafine fly ash on sulfate resistance and the influence of fly-ash fineness on alkali–silica reac- tion should be quantified in terms of the temporal evolution 𝜂(t) and its impact on bond durability, and the validated domain should be explored beyond 𝜂 > 1.

    Microstructural $$\eta$$: chemical–mechanical bridge for anchorage design in alkali–activated concretes · 2026 · DOI

  • While long-term durability under alkaline and environmental exposures warrants further study, the findings provide experimental evidence supporting the integration of bamboo reinforcement within GPC systems for eco-efficient, resilient construction.

    Sustainable reinforcement for resilient infrastructure: bamboo in geopolymer and OPC systems – mechanical and bond behavior · 2025 · DOI

  • However, limited information is available for optimising the type and amount of SCMs in binary and ternary blended SW-mixed cementitious systems for achieving desirable strength development and early-age hydration.

    Comprehensive evaluation of early-age hydration and compressive strength development in seawater-mixed binary and ternary cementitious systems · 2024 · DOI

  • Future research should focus on investigating the durability characteristics of SCMs under diverse environmental conditions, such as exposure to harsh chemicals, freeze–thaw cycles 2. Future research should investigate deeper into these constraints, examining regional differences in SCM avail- ability and the economic impact of their use in various contexts.

    Assessing the effects of supplementary cementitious materials on concrete properties:a review · 2024 · DOI

  • Calculations based on the relative site abundances of the sites observed by 29 Si NMR and the bulk chemical compositions indicate that there is insufficient alkali to charge‐balance all the non‐bridging oxygens and that there is a significant concentration of Si–OH linkages.

    Structural Investigations of Alkali Silicate Gels · 2005 · DOI

  • Steinour, “Further Studies of Bleeding of Portland Cement Paste,” Bulletin No. Powers, “A Working Hypothesis for Further Studies of Frost Resistance of Concrete,” Bulletin No. Powers, discussion of the paper, “A Working Hypothesis for Further Studies of Frost Resistance of Concrete,” Bulletin No.

    Structure and Physical Properties of Hardened Portland Cement Paste · 1958 · DOI

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62 open questions have been extracted from the limitations and future-work passages of 1,249 Concrete and Cement Materials Research papers in our library. Each one below links back to the study that raised it, so you can read the original claim in context.

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