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An important part of improving the embodied carbon of the built environment is reducing carbon emissions associated with concrete. The long-term limitations around the availability of supplementary cementitious materials (SCMs) to replace portland cement have driven the search for additional innovative approaches. The beneficial use of carbon dioxide (CO2) in ready mixed concrete production has been developed and installed as retrofit technology with industrial users. An optimum dose of CO2 added to concrete as an admixture leads to the in-place formation of mineralized calcium carbonate (CaCO3) and can increase the concrete compressive strength. The improved performance can be leveraged to design concrete mixture proportions for a more efficient use of portland cement, along with the use of CO2 to reduce the carbon footprint of concrete. One producer has used the technology, starting in 2016, at over 50 plants. More than 3 million m3 of concrete have been shipped with an estimated net savings of 35,000 tonnes of CO2. The concrete produced with carbon dioxide is discussed in terms of the fresh and hardened performance, durability performance, and life cycle impacts. [ABSTRACT FROM AUTHOR]

This paper focuses on the effects of fly ash on early-age mechanical and viscoelastic properties of concrete and on early-age cracking. Fly ash is a supplementary cementitious material that is mainly used to increase the durability of concrete. The effect on shrinkage-induced cracking of replacing some ordinary portland cement (OPC) with fly ash has not been studied previously. Material properties such as compressive strength, indirect tensile strength, and elastic modulus were measured with different percentage replacements of OPC with fly ash. Tensile creep and drying shrinkage were also measured on two types of specimens by using two different experimental techniques. The cracking age of plain concrete was observed by using a restrained ring test. Results revealed that the strength evolution of fly-ash-blended concrete is lower than the corresponding OPC concrete and the age at which restrained shrinkage cracking first occurs is also reduced. Slightly higher tensile creep coefficients were observed for fly-ash-blended concrete compared to OPC concrete, but drying shrinkage was not altered to any great extent. [ABSTRACT FROM AUTHOR]

High-performance concrete (HPC) mixtures were produced using 100% coarse recycled concrete aggregates (RCAs) from three different qualities. The concretes were produced using two binders: portland cement and portland cement with 30% of fly ash. Moreover, the fly ash mixtures underwent two different curing methods: conventional and steam curing. The effects of RCA on the physical, mechanical, and durability properties of HPC were studied for the production of prestressed elements. The natural aggregates could be completely replaced by RCA sourced from the same quality HPC. It was determined that when using lower-quality aggregates, the use of fly ash produced low 1-day compressive strength, with the consequent necessity to use steam curing to fulfill the standard requirements to be used in the production of prestressed elements. The steam curing had negative effects on the long-term mechanical properties; however, these effects were attenuated by using RCAs, which maintained their great durability. [ABSTRACT FROM AUTHOR]

To evaluate measures to prevent alkali-silica reaction (ASR) in concrete and to correlate short-term laboratory tests to longterm performance, an outdoor exposure site was established in Kingston, ON, Canada, in 1991. Alkali-silica reactive aggregate was combined into six concrete mixtures using various cements and supplementary cementitious materials (SCMs). Both unreinforced and reinforced 0.6 x 0.6 x 2 m (24 x 24 x 79 in.) beams, and 0.2 x 1.2 x 4 m (8 x 48 x 158 in.) pavement slabs were instrumented and have been monitored for 20 years. The high-alkali cement concrete cracked at 5 years and low-alkali cement cracked after 12 years. The high-alkali cement was replaced with various amounts of SCMs. Two concretes, containing 50% ground-granulated blastfurnace slag (GGBFS) and a ternary blend of 25% slag plus 3.8% silica fume interground with a high-alkali portland cement, have neither expanded nor cracked. After 14 years, cores were examined petrographically, chloride penetration profiles were made, and chloride diffusion as well as rapid chloride permeability tests, were performed. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental investigation of using phase-change materials (PCMs) in portland cement concrete. The objective of this study is to improve the thermal properties of concrete as a structural material. A compression test, flexural test, drying shrinkage test and thermal conductivity test were conducted. PCMs are used in concrete mixtures as both sand replacement and additives. The results revealed that in the replacement method, the loss of compressive strength due to the addition of PCM is not as high as the additive method. For up to 20% sand replacement by PCM, the strength loss is not significant for structural applications. The specific heat of the concrete increased considerably. Thus, the thermal conductivity of the concrete is reduced and the insulation capacity of the concrete is improved. A flexural test, drying shrinkage test, and microstructure analysis provide a good understanding of the PCM-modified concrete. Overall, the results show that it is quite promising to use PCM in concrete to improve its insulation capacity with decreased thermal conductivity and, at the same time, that it is possible to keep the strength loss of the concrete in an acceptable range. [ABSTRACT FROM AUTHOR]

This paper addresses the permeation properties of self-consolidating concretes (SCCs) with different types and amounts of mineral admixtures. Portland cement (PC), metakaolin (MK), fly ash (FA), and ground-granulated blast-furnace slag (GGBFS) were used in binary, ternary, and quaternary cementitious blends to improve the durability characteristics of SCCs. For this, a total of 22 SCCs were designed that have a constant water-binder ratio (w/b) of 0.32 and a cementitious materials content of 926.75 lb/yd3 (550 kg/m3). In addition to compressive strength and ultrasonic pulse velocity, the permeation resistance of SCCs was determined by means of chloride ion permeability, water permeability, and sorptivity tests. The test results indicated that the permeation properties of SCCs appeared to be very dependent on the type and amount of the mineral admixture used; the SCC mixtures containing MK were found to have considerably higher permeability resistance than the control mixture. [ABSTRACT FROM AUTHOR]

The article provides information on a research about the fundamental aspects that result from using mineral admixtures in high-performance concrete (HPC). It focuses on the impact of various pozzolanic admixtures on the process of pore network refinement. It states that HPC is known for the refinement of its capillaries' pores, which induces two opposite phenomena such as improved mechanical performances and self-dessication shrinkage due to high capillary depression. It discusses cement hydration reaction from solid products and a pore system. The study used mercury intrusion porosimetry (MIP) to determine the porosity and pore size distribution of concrete. Results show that refinement of the capillary network and evolution with time are linked with mineral addition type and fineness.

This study examines whether cellulose nanocrystals (CNCs) can be used in ordinary portland cement (OPC)-limestone (LS) systems to reduce the carbon footprint of concrete. LS replacement levels between 0 and 30% were evaluated along with CNC dosage rates between 0 and 1% CNC solids per binder volume. Isothermal calorimetry, thermogravimetric analysis, ball-on-three-ball flexural strength, and electrical resistivity tests were used to quantify the performance of the mixtures. The results showed that the addition of CNCs to OPC-LS mixtures resulted in enhanced clinker hydration and up to a 38% increase in the 28-day bulk resistivity. It is demonstrated that a mixture for which 22% of the OPC was replaced with LS and containing 0.2% CNC had an equivalent performance in terms of transport properties compared to the 100% OPC system. This could potentially reduce embodied carbon content by approximately 19.4% when compared to the pure OPC system. [ABSTRACT FROM AUTHOR]