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Ternary blended cements, made with silica fume and limestone, provide significant benefits such as improved compressive strength, chloride penetration resistance, sulfates attack, etc. Furthermore, they could be considered low-carbon cements, and they contribute to reducing the depletion of natural resources in reference to water usage, fossil fuel consumption, and mining. Limestone (10%, 15%, and 20%) with different fineness and coarse silica fume (3%, 5%, and 7%) was used to produce ternary cements. The average size of coarse silica fume used was 238 μm. For the first time, the carbonation resistance of ternary Portland cements made with silica fume and limestone has been assessed. The carbonation resistance was assessed by natural carbonation testing. The presence of coarse silica fume and limestone in the blended cement led to pore refinement of the cement-based materials by the filling effect and the C-S-H gel formation. Accordingly, the carbonation resistance of these new ternary cements was less poor than expected for blended cements.

The alkali-silica reaction has been studied in depth due to the evolution in the knowledge of the expansive phenomenon. One of its most important aspects is the reaction rate of the aggregates. In Spain, at the early 90s of the 20th century, aggregates were considered almost non-reactive. However, the use of accelerated curing and other environmental factors revealed that there were potentially reactive siliceous aggregates. Nevertheless, there are several siliceous and limestone aggregates with siliceous inclusions that show reactivity over long period. In the present work, open porosity, expansion and petrography with quartz reactivity index have been determined, in 68 siliceous, limestone and dolomitic aggregates, from quarries located in areas with diagnostic reactivity. Based on these parameters and their interrelation, a classification method is proposed to detect slow-reacting aggregates.

Portland cement production is an energy-intensive process that releases carbon dioxide into the atmosphere. To reach carbon neutrality by 2050, it would be necessary to implement innovative measures in the cement industry to deliver carbon neutrality. In this respect, it is striking that the new cement types made with high contents of industrial by-products will act as a lever to combat climate change. Accordingly, the purpose of this study is to assess coal–ash blended cements in light of climate change mitigation. In particular, ground coal bottom ash could be considered as a novel constituent for common cement production. The performance of these coal–ash mortars was assessed by measuring pozzolanic reactivity, mechanical strength gain, and microstructural characteristics. Mortars were made with 10%, 25%, or 35% of coal ash (fly ash and/or bottom ash). Therefore, by considering an emission intensity factor of 830 kgCO2/kg of clinker, a reduction in carbon dioxide emissions for all coal fly ash cements is expected, which will be about 83 kgCO2/kg of cement, 208 kgCO2/kg of cement, and 290 kgCO2/kg of cement, respectively. Ground coal bottom ash presented similar characteristics to the coal fly ash. Consequently, ground coal bottom ash is a promising Portland cement constituent with properties comparable to coal fly ash, and its increased usage can contribute to the climate change mitigation.

Ternary Portland cements composed of coarse silica fume (SF), limestone (LS), and Portland cement (PC) can afford some environmental advantages by reducing the clinker content in Portland cements. These cements will help to reduce the clinker factor target from 0.78 to 0.60 by 2050 with the aim to be climate neutral. Silica fume (SF) possesses pozzolanic properties that enhance mechanical strength and durability. By contrast, limestone powder has three main outcomes, i.e., filler, dilution, and chemical effects. The first reduces porosity and refines the microstructure of mortars and concretes. The second decreases the amount of hydration products and increases the porosity; the third one promotes the appearance of carboaluminates and reduces porosity. This paper covers the mechanical properties of Portland cement-limestone-coarse silica fume ternary cements, and its synergetic mechanism. Compressive and flexural strength of mortar at 2, 7, 14 and 28 days was performed. Coarse silica fume has a minor contribution on the nucleation effect compared to ground limestone at early ages. The nucleation and filler effects, at early ages, are less pronounced in coarse and very fine limestone powder. The highest compressive strength at 28 days is reached with the lowest content of coarse silica fume (3%). Mortar mixes made with a high level of limestone presented a delay in the compressive strength development.

Alkali–silica reaction (ASR) is a swelling reaction that occurs in concrete structures over time between the reactive amorphous siliceous aggregate particles and the hydroxyl ions of the hardened concrete pore solution. The aim of this paper is to assess the effect of pozzolanic Portland cements on the alkali–silica reaction (ASR) evaluated from two different points of view: (i) alkali-silica reaction (ASR) abatement and (ii) climatic change mitigation by clinker reduction, i.e., by depleting its emissions. Open porosity, SEM microscopy, compressive strength and ASR-expansion measurements were performed in mortars made with silica fume, siliceous coal fly ash, natural pozzolan and blast-furnace slag. The main contributions are as follows: (i) the higher the content of reactive silica in the pozzolanic material, the greater the ASR inhibition level; (ii) silica fume and coal fly ash are the best Portland cement constituents for ASR mitigation.

The increased use of industrial wastes and by-products to produce concretes and blended cements is a lever to achieve carbon neutrality. Furthermore, they could improve their durability. Some pozzolanic additions can minimize the alkali-silica reaction (ASR), which is a well-known deleterious process that occurs between some reactive aggregates and the alkaline pore solution found in mortars and concretes. This work quantifies the efficiency of four pozzolanic materials (natural pozzolan, P, siliceous coal fly ash, V, silica fume, D, and blast-furnace slag, S) assessed by means of compressive strength testing, open porosity, ASR-expansion measurements, and SEM microscopy. Accelerated expansion tests were performed in mortar bars with a cement/sand ratio of 1/2.25 and a water/cement ratio of 0.47, two reactive aggregates and a non-reactive one. The major contributions of this paper are: (i) The more aggregate reactivity is, the higher ASR mitigation level was found when additions were added and (ii) The best additions for ASR inhibition are silica fume and fly ash.