Tests to determine the reactivity of supplementary cementitious materials (SCMs) by using isothermal calorimetry and thermogravimetric analysis have been proposed. In one such test, the heat release ...and calcium hydroxide consumption of SCMs mixed with calcium hydroxide (3:1 ratio of calcium hydroxide and SCM) at 50 °C in a 0.5 M potassium hydroxide environment are measured. In this study, we show the results of such testing for a large variety of SCMs and fillers, ranging from conventional materials such as fly ash, slag, silica fume, quartz, and limestone, to alternative materials such as calcined clays, municipal solid waste incineration fly ash, basic oxygen furnace slag, ground lightweight aggregates, ground pumice, ground glass pozzolan, and basalt fines. A total of 54 SCMs are tested using this approach. Results show that even among SCMs of the same type, there is considerable difference in the heat release and calcium hydroxide consumption, likely due to differences in amorphous content, chemical composition, and fineness, leading to different reactivities. Based on the response in the test, SCMs are classified into inert, pozzolanic, and latent hydraulic; the pozzolanic and latent hydraulic materials are further classified into less reactive and more reactive. The relationship between heat release and calcium hydroxide consumption depends on the chemical composition of the SCMs, and SCMs with high calcium, high alumina, and high silica contents show different relationships (determined by the slope of the heat release vs. calcium hydroxide plot).
In this work, the negative impacts of calcium sulfoaluminate (CSA) cement prehydration on hydration and strength gain are investigated. CSA cement in three different states – virgin, prehydrated, and ...prehydrated and sieved were tested. Cement paste mixtures were made with three levels of ordinary portland cement (OPC) – 0%, 30%, and 70% (indicating the percentage of OPC in total cementitious material) at a water-to-cementitious materials ratio of 0.40. CSA cement prehydration causes an increase in the particle size measured by laser diffraction, the presence of elongated particles in the electron micrograph, and the detection of hydrated and carbonated phases using thermogravimetric analysis. Prehydration of CSA cement has detrimental effects on hydration and strength gain on CSA-OPC mixtures, with exact effects depending strongly on the OPC level in the cement paste. In mixtures with 70% OPC, the effect of prehydration is pronounced – heat release of the mixture with virgin CSA cement at seven days is 33% higher than in the mixture with prehydrated CSA cement and the corresponding strength at 28 days is 196% higher. Relationships between heat release, bound water, and compressive strength and the effect of prehydration on these relationships were also explored. Sieving the prehydrated CSA cement before use presents some limited benefits in the reducing the detrimental effects of prehydration.
•Concrete and GFRP from 18-year old dry-dock repair analyzed.•Concrete shows variability and clear degradation.•GFRP variability limited and degradation limited to surface.•GFRP can be a potential ...alternative to steel for marine structures.
Concrete and glass fiber reinforced polymer (GFRP) bar samples from an 18-year old repair project executed on an existing dry-dock were obtained by coring the dry dock in two regions. Several destructive and non-destructive tests were performed on both materials. Testing performed on the concrete showed substantial variability and clear evidence of damage occurring over the years. Further, there were significant differences in the concrete obtained from two different regions of the dock. The concrete was carbonated and chloride from seawater had penetrated significantly into its depth. The GFRP bars showed relatively lower variability in terms of test results. Electron microscopy and horizontal shear strength results suggest that the GFRP surface of the bars had suffered some damage, whereas the core had remained unaltered. These findings regarding limited damage to the GFRP, taken together with recent advances in GFRP production technology, support the notion that concrete reinforced with GFRP bars is an attractive alternative to conventional steel reinforced concrete for marine infrastructure applications.
The influence of supplementary cementitious materials (SCMs) and filler fineness on their reactivity in model systems and in cementitious pastes was evaluated. Two SCMs–pumice (P), and glass powder ...(GP), and an inert filler–limestone (LS), with three different levels of fineness and median particle size (d
50
) values were tested using the modified R
3
test to obtain direct measures of their reactivity. The reactivity of P and GP, indicated by the heat release and calcium hydroxide consumption, increased linearly as the d
50
decreased (and fineness increased). However, for LS, the change in fineness did not influence the reactivity. These materials were used at a 30% replacement level by mass in cementitious pastes at a water-to-cementitious materials ratio of 0.40 and heat release, calcium hydroxide content, compressive strength, and bulk resistivity were monitored. The increasing fineness impacted property development in very similar ways for the P and the GP but not for the LS. For the SCMs, early- and later-age properties generally, but not always, had a linear correlation with median particle size. Bulk resistivity was a notable exception, with early-age values not depending on median particle size and later-age values showing a non-linear relationship with median particle size. For coarser materials, the impacts were largely driven by dilution and filler effect, but for finer materials, the impact of reactivity on property development was evident. The effects of SCM reactivity were more evident at later ages. The heat release and calcium hydroxide consumption measured in the modified R
3
test were correlated to the 56-day calcium hydroxide content, compressive strength, and bulk resistivity in cementitious pastes.
The feasibility of using a muffle furnace and a balance to determine the calcium hydroxide (Ca(OH)
2
) consumption of supplementary cementitious materials (SCMs) in model systems was investigated. ...SCMs were mixed with Ca(OH)
2
in an alkaline solution and, after mixing, the paste was sealed inside a 50 °C oven for curing until testing. The chemically bound water and Ca(OH)
2
consumption were determined using the furnace at two fixed temperatures and the results were compared with those from the thermogravimetric analysis. The protocol of the furnace test was optimized based on thermogravimetric analysis results. While further testing is needed, initial results demonstrated the validity of the method, and suggest that it is able to differentiate inert, latent hydraulic, and pozzolanic materials using reactivity thresholds for the chemically bound water and the Ca(OH)
2
consumption. This new test could be used for rapid and low-cost screening of novel SCMs.
Blast furnace slag (SL) is an amorphous calcium aluminosilicate material that exhibits both pozzolanic and latent hydraulic activities. It has been successfully used to reduce the heat of hydration ...in mass concrete. However, SL currently available in the market generally experiences pre-treatment to increase its reactivity to be closer to that of portland cement. Therefore, using such pre-treated SL may not be applicable for reducing the heat of hydration in mass concrete. In this work, the adiabatic and semi-adiabatic temperature rise of concretes with 20% and 40% SL (mass replacement of cement) containing calcium sulfate were investigated. Isothermal calorimetry and thermal analysis (TGA) were used to study the hydration kinetics of cement paste at 23 and 50 °C. Results were compared with those with control cement and 20% replacements of silica fume, fly ash, and metakaolin. Results obtained from adiabatic calorimetry and isothermal calorimetry testing showed that the concrete with SL had somewhat higher maximum temperature rise and heat release compared to other materials, regardless of SL replacement levels. However, there was a delay in time to reach maximum temperature with increasing SL replacement level. At 50 °C, a significant acceleration was observed for SL, which is more likely related to the pozzolanic reaction than the hydraulic reaction. Semi-adiabatic calorimetry did not show a greater temperature rise for the SL compared to other materials; the differences in results between semi-adiabatic and adiabatic calorimetry are important and should be noted. Based on these results, it is concluded that the use of blast furnace slag should be carefully considered if used for mass concrete applications.
Two mine tailings are evaluated for their potential as supplementary cementitious materials. The mine tailings were milled using two different methods – ball milling for 30 minutes and disc milling ...for durations ranging from 1 to 15 minutes. The modified R3 test was carried out on the mine tailings to quantify their reactivity. The reactivity of the disc milled tailings is greater than those of the ball milled tailings. Strong correlations are obtained between milling duration, median particle size, amorphous content, dissolved aluminum and silicon, and reactivity of the mine tailings. The milling energy results in an increase in the fineness and the amorphous content, which do not appreciably increase beyond a disc milling duration of 8 minutes. The reactivity increases significantly beyond a certain threshold fineness and amorphous content. Cementitious pastes were prepared at 30% supplementary cementitious materials replacement level at a water-to-cementitious materials ratio of 0.40. No negative effects of the mine tailings were observed at early ages in cement pastes based on isothermal calorimetry and thermogravimetric analysis, demonstrating the potential for these materials to be used as supplementary cementitious materials.
This work characterizes the reaction kinetics of supplementary cementitious materials (SCMs) with calcium hydroxide in the modified R3 test. The heat flow curves of 58 SCMs of varying reactivities ...were studied. Based on the heat flow curves, the SCMs were classified as more reactive, less reactive, and inert. Most of the heat flow curves in the modified R3 test exhibit, after the peak of heat flow, an initial slow decaying power-law regime that transitions into a longer and faster decaying power-law regime. The pre-exponent of the first regime depends on the initial SCM reactivity and correlates well with the 24-hour heat release in the modified R3 test, thus making it a useful metric for rapid classification of SCMs.
The review summarises literature to examine the transition from portland limestone cement system to composite ternary binder systems involving limestone. Interest in limestone addition as an ideal ...component in multicomponent binder systems has surged as evident from the large volume of literature published in the recent past. A ternary blended system, with co-substitution of limestone, has the potential to complement the reaction of the supplementary cementitious materials (SCMs). The direct addition of limestone powder helps to attain higher substitution levels of portland cement clinker, improve early age properties, and supplement SCM's reactivity. However, the dilution of hydrates could hamper the long-term benefits. In this review, the interaction of fine limestone is classified and elaborated under two broad umbrellas: physical and chemical interactions. The physical interactions can manifest in three ways, namely, filler action, shearing action and improved packing, which alters reaction rate and extent at early ages. The chemical interactions also modify the reaction kinetics and phase assemblage due to nucleation of C-S-H on calcite surfaces, preservation of the ettringite phase and formation of carboaluminates. Two different forms of carboaluminate hydrates — hemicarboaluminate and mono-carboaluminate can be present in the hydrate matrix depending on the balance between carbonate ions and aluminates in the pore solution. Several factors such as replacement level, particle size, choice of SCM, its reactivity and reactive aluminates content, sulphate levels, curing temperature, and duration of curing can control the carboaluminate formation, reaction degree of SCMs and chemical interaction from limestone additions.
A combination of physical and chemical effects makes fine limestone a potential material for co-substitution with aluminosilicate based SCMs, mainly fly ash, slag, and calcined clay. In this review, the factors affecting limestone-SCM composites are summarised based on a detailed literature survey. The effects of SCM-limestone cement composites on hydration kinetics, reaction chemistry, the reactivity of SCMs, the stability of hydrated phases, and contribution to the physical structure development and macroscopic properties by evaluating hydration and mechanical properties are discussed. The importance of AFm (Al2O3–Fe2O3-mono) phases in various deterioration mechanisms in concrete and their influence on performance characteristics in different exposure environment is critically appraised.
Modified R3 testing has been used to classify four different SCMs, namely, limestone, pumice, slag, and densified silica fume. Cementitious pastes were prepared by replacing ordinary portland cement ...with SCMs at different replacement levels – 20%, 40%, and 60% for limestone, pumice, and slag and 5%, 10%, and 15% for silica fume. The influences of SCM replacement level on heat flow, heat release, calcium hydroxide consumption, bound water contents, compressive strength, and bulk resistivity for a period of 56 days were quantified. The SCMs have widely varying effects on these properties as a function of replacement levels, however, in general, inert and reactive SCMs show little difference in properties at early ages and lower replacement levels (20%). The impacts of SCMs on cementitious paste properties are more apparent at higher replacement levels (40%–60%) and at later ages (28 and 56 days). These findings have important implications in practice and suggest that standard ASTM strength activity index testing could be improved by testing at higher replacement levels. In addition, bulk resistivity shows ability to differentiate inert and reactive materials and could be a potential candidate for standardization. The ratio of heat release to calcium hydroxide consumption obtained from the modified R3 test shows a strong correlation with the relative compressive strength of SCMs at different replacement levels and could be used to explore links between reactivity testing, SCM replacement, and paste property evolution.
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