Working Group 1 of RILEM TC 238-SCM ‘Hydration and microstructure of concrete with supplementary cementitious materials (SCMs)’ is defining best practices for the physical and chemical characterization of SCMs, and this paper focusses on their thermal analysis. Thermogravimetric analysis (TGA) can provide valuable data on the chemical and mineralogical composition of SCMs. Loss-on-ignition (LOI) testing is a commonly used, standardized, but less sophisticated version of TGA that measures mass at endpoints only, with heating generally in air. In this paper we describe the use of TGA and LOI to characterize Portland cement with limestone additions, coal combustion fly ashes, ground-granulated blast furnace slag, calcined clays, and natural pozzolans. This paper outlines the value and limitations of TGA and LOI (in the formats defined in different standards regimes) for material characterization, and describes testing methods and analysis. TGA testing parameters affect the mass loss recorded at temperatures relevant for LOI measurements (700–1000 °C) of slags and fly ashes, mainly associated with oxidation reactions taking place upon heating. TGA of clays and natural pozzolans is utilized to identify optimal calcination conditions leading to dehydroxylation and consequent structural amorphization, particularly for kaolinite. However, dehydroxylation and amorphization do not occur at similar temperatures for all clays, limiting the applicability of TGA for this purpose. Although TGA is widely utilized for characterization of SCMs, the testing parameters significantly affect the results obtained, and TGA results require careful interpretation. Therefore, standardization of TGA testing conditions, particularly for LOI determination of slags and fly ashes, is required.

A critical area overlooked in previous research on pumice is understanding how its physical characteristics influence its behavior as a supplementary cementitious material (SCM). This study investigated three pumices with different particle size distributions to observe whether these porous materials exhibit enhanced nucleation and growth of hydration products, in the same way as non-porous materials, and whether the rate of pozzolanic reaction can be changed through particle size. The effect of particle size on compressive strength, rheology and resistance to alkali silica reaction (ASR) was also evaluated. Results showed that reducing particle size increased the rates of cement hydration, pozzolanic reaction, and compressive strength gain, while also increasing mixture viscosity. Interestingly, particle size did not impact the yield stress of the mixture or the resistance to ASR. These new findings give insight about how the particle size of pumice can be used to overcome drawbacks reported in previous literature.

This work examined the effects of milling using a gravity ball mill on the reactivity of natural zeolites used as supplementary cementitious materials (SCMs). Six different particle size distributions of zeolites, created by milling the as-received zeolite in a ball mill for a specified amount of time, were characterized using x-ray fluorescence, quantitative x-ray diffraction, particle size analysis, pore size distribution and surface area analysis. Following material characterization, the pozzolanic reactivity of the zeolites was determined by measuring the quantity of calcium hydroxide in paste after 28 or 90 days and by tracking the compressive strength of zeolite-cement mortars. Results showed that a critical milling time exists, corresponding to a d50 of 7–9 μm, after which reductions in particle size can no longer be achieved and zeolite performance can no longer be improved through ball milling.

Oxides of nitrogen (NOx) are ubiquitous pollutants in large urban areas of the world. Photocatalytic materials have been studied, primarily in the laboratory, for their ability to remove oxides of nitrogen. The study described herein compared NOx removal efficacies of three commercially-available photocatalytic coatings (a stucco, a white paint and a clear paint) applied to roadside concrete. The study aimed to elucidate how environmental parameters and exposure to real roadside conditions impact NOx removal. This was achieved through periodic laboratory chamber testing and material characterization of concrete slabs stored by busy roadways for a 20-month period. It was observed that roadside exposure led to physical degradation of the clear paint coating, while the other two remained intact. The stucco coating was the most effective at NOx removal, but the efficacy nonetheless diminished over time.

Reply to the discussion of the paper “Understanding expansion in calcium sulfoaluminatebelite cements” by G.L. Valenti, M. Marroccoli, M.L. Pace, A. Telesca.

Calcium sulfoaluminate–belite (CSAB) cements are promoted as sustainable alternatives to portland cement because of their lower energy and CO2 emissions during production and comparable performance. However, the formation of ettringite, the main hydration product in CSAB cements, can be expansive, sometimes resulting in cracking. The factors controlling expansive behavior in CSAB cements have not been completely elucidated. In this study, three CSAB cements synthesized from reagent-grade chemicals with varied phase compositions were examined for dimensional stability in water and sulfate solutions. The interdependent effects of C4A3Ŝ (Ye'elimite) content, calcium sulfate content, water-to-cement ratio, and particle fineness on CSAB cement expansion were evaluated. The results show that the expansive behavior can be controlled by altering chemical and physical factors in CSAB clinker, cement, and paste.

In recent years, calcium sulfoaluminate-belite (CSAB) cement has been promoted as a sustainable alternative to Portland cement due to lower energy used and less CO2 emitted during production, while providing comparable performance. However, a potential problem facing the widespread adoption and production of CSAB cement is the cost and availability of raw materials and it is therefore desirable to find alternative raw materials to keep costs competitive. In this study, two CSAB cement clinkers with a similar target phase composition were synthesized from combinations of natural and waste materials (coal combustion residuals). The two CSAB cement clinkers were compared against a CSAB clinker made from reagent-grade chemicals, enabling examination of the effects of impurities on performance. Cements made from the clinkers were examined for hydration rate, hydration product formation, dimensional stability, and compressive strength.

There is a burgeoning interest in the development, characterization, and implementation of alternatives to Portland cement as a binder in concrete. The construction materials industry is under increasing pressure to reduce the energy used in production of Portland cement clinker and the associated greenhouse gas emissions. Further, Portland cement is not the ideal binder for all construction applications, as it suffers from durability problems in particularly aggressive environments. Several alternative binders have been available for almost as long as Portland cement, yet have not been extensively used, and new ones are being developed. In this paper, four promising binders available as alternatives to Portland cement are discussed, namely calcium aluminate cement, calcium sulfoaluminate cement, alkali-activated binders, and supersulfated cements. The history of the binders, their compositions and reaction mechanisms, benefits and drawbacks, unanswered questions, and primary challenges are described.

This paper describes the application of low temperature scanning electron microscopy to the materials science of Portland cement. The details of low-temperature scanning electron microscopy are described, along with a number of specimen preparation techniques. There are three main research topics presented in this paper: (1) ice morphology in entrained air voids, (2) development of air voids during early hydration and (3) progression of hydration in Portland cement. The first research focus examines ice in air voids at freezing temperatures, and various cement paste ages. The second research focus tracks the development of the air voids during the first hour of hydration. In the third research focus, the progression of hydration with and without accelerating and retarding admixtures is described. Each of these research programs demonstrates how low-temperature scanning electron microscopy can be an effective tool in Portland cement research.