This article reviews the challenges in the rational use of limestone and supplementary cementitious materials in the optimization of low carbon cement and concrete with machine learning (ML), and introduces preliminary results of the corresponding program of research at HeidelbergMaterials.

The mining of the Global R&D database showed that the main challenge was not the algorithm type—the general linear model performed as well as artificial networks—but the underlying dataset quality, the rational design of the experiment in the face of the high dimensionality of the problem, and the model testing methodology.

Preliminary results of show that a clinker ratio as low as 50% can be obtained at equal or better strength and workability performance. The surface area of limestone and aggregates was found to be as important as their weight proportion on rheology and early age properties. Regarding the predictors of early age strength, the best subset selection method identified no less than seven variables in addition to C3S and Blaine fineness. The prediction model thus identified a CEM I composition that could reach 50 MPa in one day, thus paving the way to higher SCM replacement levels.

Although limestone calcined clay cement (LC³) is a valid alternative to reduce the carbon footprint of cement production, some of its properties, like workability, still need to be investigated and fully understood. In this work, different cement pastes containing variable amounts of calcined clay with and without superplasticizer were analyzed. Measurements at the rheometer scale were performed to evaluate the superplasticizer’s effect on the samples’ workability. The amount of free water available after 1 hour of hydration in cement pastes was detected by Differential Scanning Calorimetry (DSC). Moreover, the Time-Domain Nuclear Magnetic Resonance (TD-NMR) was used to identify whether this water was contained either in capillary pores or in interhydrate spaces. The results obtained by DSC and TD-NMR revealed that pastes containing superplasticizers show a slightly higher amount of available free water, with a direct positive consequence on rheological properties. However, the amount of calcined clay (CC) in cement impacts both aspects: superplasticizer dosage to reach the target fluidity of pastes and workability retention over 60 minutes. Moreover, the confirmation of the exponential correlation between yield stress and the solid content of cementitious particles is possible when considering the detected capillary water as an indicator of the normalized concentration of solid particles.

In recent years, there has been a growing need to develop eco-efficient concrete with reduced cement content for sustainable construction practices. This paper aims to highlight the importance of the concrete net zero goal by 2050 and explore how concrete particle-packing models and limestone fillers can contribute to achieving sustainable targets. Four eco-efficient concrete mixtures with varying cement content (320, 250, 200, and 150 kg/m³) were developed. A comprehensive analysis of the hardened state properties, including surface electrical resistivity, compressive strength, and modulus of elasticity, was conducted over time for each mixture. Furthermore, this paper briefly discusses methods to analyze concrete eco-efficiency and their impact on global warming. The results presented in this study contribute to the understanding of the importance of concrete eco-efficiency and provide insights for engineers and researchers on how to evaluate concrete eco-efficiency.

This paper examines the influence of harvested fly ash on the properties of mortar and concrete. Class F and harvested fly ash were used at the substitution rate of 20% by weight of Portland cement. The investigated properties included heat release, consistency, setting time, compressive strength at different testing ages, absorption, the volume of permeable voids, surface resistivity, and drying shrinkage. The results revealed that the harvested fly ash produced the lowest released heat of hydration and longest setting times. Mixtures containing harvested fly ash displayed lower strength at all curing ages. Compared to traditional fly ash, harvested fly ash showed inferior transport properties for both absorption rate, permeable voids, and surface resistivity. Mixtures containing harvested fly ash showed comparable 120-day drying shrinkage when compared with the companion mortars made with traditional fly ash.

Due to its predominant soda-lime composition, most post-consumer glass processed by recycling facilities would be classified as high-alkali pozzolanic glass powder (GP). In cementitious matrices, the intrinsic alkaline pore solution induces the dissolution of both silica and alkali ions. Therefore, the GP can potentially induce two similar reactions in concrete: either a deleterious alkali-silica reaction or a pozzolanic reaction. The equilibrium of the pore solution will determine which reaction will prevail in the long term. To understand the chemical stability of GP in a cementitious system, the evolution of the solubility of key elements in an alkali-rich synthetic pore solution was studied as a function of reaction time, particle size, presence of Ca(OH)₂ and CaCO₃, and binder/solution ratio (B/S). The solution was based on the R³ method, which consists mainly of lab-grade chemicals such as KOH and K₂SO₄. Although the chemical equilibrium seems to be fully reached in the first hours of hydration, the main products, such as C-S-H, are unstable because the alkali leaching/uptake in the C-S-H chains is dynamically evolving. The experiments show that both C-S-H precipitation and alkali leaching rates increase with increasing B/S ratio and decreasing particle size, and are directly related to the presence of calcium in the solution.