Supplementary cementitious materials: New sources, characterization, and performance insights

Conventional supplementary cementitious materials (SCMs), such as blast furnace slags or fly ashes, have been used for many decades, and a large body of knowledge has been collected regarding their compositional make-up and their impacts on cement hydration and concrete properties. This accumulated empirical experience can provide a solid, confident base to go beyond the status quo and develop a new generation of low-clinker cements composed of new types and combinations of SCMs. The need for new sources of SCMs has never been greater, as supplies of traditional SCMs are becoming restricted, and the demand for SCMs to reduce CO2 emissions from concrete production is increasing. In this paper, recent research on emerging SCM sources is reviewed, along with new developments in characterizing and qualifying SCMs for use and improved knowledge of SCMs on long-term concrete performance and durability

Fracture properties of GGBFS-blended fly ash geopolymer concrete cured in ambient temperature

Fracture characteristics are important part of concrete design against brittle failure. Recently, fly ash geopolymer binder is gaining significant interest as a greener alternative to traditional ordinary Portland cement (OPC). Hence it is important to understand the failure behaviour of fly ash based geopolymers for safe design of structures built with such materials. This paper presents the fracture properties of ambient-cured geopolymer concrete (GPC). Notched beam specimens of GPC mixtures based mainly on fly ash and a small percentage of ground granulated blast furnace slag were subjected to three-point bending test to evaluate fracture behaviour. The effect of mixture proportions on the fracture properties were compared with control as well as OPC concrete. The results show that fracture properties are influenced by the mixture compositions. Presence of additional water affected fracture properties adversely. Fracture energy is generally governed by tensile strength which correlates with compressive strength. Critical stress intensity factor varies with the variation of flexural strength. Geopolymer concrete specimens showed similar load–deflection behaviour as OPC concrete specimens. The ambient cured GPC showed relatively more ductility than the previously reported heat cured GPC, which is comparable to the OPC specimens. Fly ash based GPC achieved relatively higher fracture energy and similar values of KIC as compared to those of OPC concrete of similar compressive strength. Thus, fly ash based GPC designed for curing in ambient condition can achieve fracture properties comparable to those of normal OPC concrete

Report of RILEM TC 267-TRM phase 2: optimization and testing of the robustness of the R3 reactivity tests for supplementary cementitious materials

The results of phase 1 of an interlaboratory test, coordinated by the RILEM TC 267-TRM “Tests for Reactivity of Supplementary Cementitious Materials” showed that the R3 (rapid, relevant, reliable) test method, by measurement of heat release or bound water, provided the most reliable and relevant determination of the chemical reactivity of supplementary cementitious materials (SCMs), compared to other test methods. The phase 2 work, described in this paper aimed to improve the robustness of the test procedure and to develop precision statements for the consolidated test procedure. The effect of the pre-mixing and mixing conditions, and the impact of the mix design on the test method robustness were assessed and fixed for optimal conditions to carry out the R3 heat release test. The effect of the drying step was evaluated to define the R3 bound water test procedure in more detail. Finally, the robustness of the consolidated final test methods was determined by an interlaboratory study to define the precision statements

Influence of fly ash blending on hydration and physical behavior of Belite-Alite-Ye'elimite cements

A cement powder, composed of belite, alite and ye’elimite, was blended with 0, 15 and 30 wt% of fly ash and the resulting lended cements were further characterized. During hydration, the presence of fly ash caused the partial inhibition of both AFt degradation and belite reactivity, even after 180 days. The compressive strength of the corresponding mortars increased by increasing the fly ash content (68, 73 and 82 MPa for mortars with 0, 15 and 30 wt% of fly ash, respectively, at 180 curing days), mainly due to the diminishing porosity and pore size values. Although pozzolanic reaction has not been directly proved there are indirect evidences.This work is part of the Ph.D. of D. Londono-Zuluaga funded by Beca Colciencias 646—Doctorado en el exterior and Enlaza Mundos 2013 program grant. Cement and Building materials group (CEMATCO) from National University of Colombia is acknowledged for providing the calorimetric measurements. Funding from Spanish MINECO BIA2017-82391-R and I3 (IEDI-2016-0079) grants, co-funded by FEDER, are acknowledged

Internal Curing Using Superabsorbent Polymers for Alkali Activated Slag-Fly Ash Mixtures

Increased shrinkage is often noted as a concern for alkali activated materials. In this study, two slag-fly ash paste and mortar mixtures with slag:fly ash ratios of 30:70 and 50:50 activated using 4M sodium hydroxide are formulated. The effects of two dosages of a commercial superabsorbent polymer (SAP) on the reaction heat, strength gain, autogenous shrinkage, drying shrinkage, and mass loss behavior are presented here. The SAP increases the heat of reaction of the alkali activated pastes, however, this increase is less than 5% at 7 days. The SAP slightly decreases the compressive strength of the alkali activated mortars, and this decrease is generally less than 10% at 1, 7, and 28 days. The SAP significantly reduces the ultimate autogenous shrinkage (by more than 50%) and reduces the drying shrinkage (by 15–30%) of the mortars. Mixtures with SAP have autogenous shrinkage between 50–300 με and drying shrinkage between 600–700 με. When SAP is used, the mass loss in the mortars increases, however, the slope of the mass loss-drying shrinkage curve decreases. Shrinkage mitigation in the studied mixtures increases as the SAP dosage increases. Further studies on this system, and on other binders, activator combinations, and SAP types are currently ongoing

Impact of Liquid Whey Waste on Strength and Stiffness of Cement Treated Clay

The reuse of whey waste, a by-product of the dairy industry, is an emerging issue due to the environmental impacts. Some previous experimental studies have indicated that whey waste can be used as an admixture for cement-based materials, including mortar and concrete, to reduce the setting time and increase the workability, thus reduce the amount of required cement. However, influence of whey waste on cemented soil has not received sufficient attention. This study investigates variations of unconfined compressive strength (UCS) and Young's modulus (E) of cemented Kaolin clay when water in cement slurry was replaced by different whey waste proportions. Unconfined compression tests were conducted on treated specimens after two different curing times, namely 14 days and 56 days. Stress-strain relationship in each test was used to compute UCS and E at different dosages of cement and whey waste. Results of the experiments show improvements of UCS and E only for specimens when less than 10% water in cement slurry was replaced by liquid whey waste at 56 day-curing age, regardless of cement dosage. For the other cases, the presence of whey waste resulted in reductions of both UCS and E, indicating that although whey waste can be used to improve mechanical properties of cement treated clay, the optimum dosage should be selected very carefully to minimize the adverse effects. Different responses of UCS and E with curing age, dosages of cement and liquid whey waste are explained while discussing about the effects of lactose (milk sugar) available in whey waste acting as a retarding agent

Sustainable Concretes for Structural Applications

For the production of a high-performance concrete (HPC) matrix, a large amount of binder is normally used. The production of ordinary Portland cement (OPC) as the binder of concrete accounts for 7% of CO2 emission, which has notable environmental impacts, and subsequently results in unsustainable concrete. The aim of the present study was to investigate the effect of replacing OPC with calcium sulfoaluminate cement (CSA) or ground granulated blast-furnace slag (GGBS) as sustainable binders on the engineering properties of HPC. Additionally, the effect of introducing double hooked-end (DHE) steel fibers at a fiber volume fraction of 1% on the properties of HPC was assessed. The compressive strength, splitting tensile strength, flexural strength, and modulus of elasticity of HPC were evaluated. Moreover, a scanning electron microscopy (SEM) method was used to study the microstructure of the concretes. The results indicate that the replacement of OPC with CSA cement results in an improvement in the mechanical properties of HPC particularly at later ages of curing, while combination CSA cement with OPC and GGBS in the binary and ternary systems degrades the concrete’s strengths. The addition of 1% DHE steel fibers significantly increased the engineering properties of concrete. The results show that the bond between a cement matrix and steel fibers has been enhanced due to the expansive behavior of CSA cement. The SEM observation also shows the significant influence of CSA cement on the microstructure of concrete by forming a rich amount of ettringite which subsequently results in an improvement in the properties of concrete