•Hydraulic and pozzolanic behavior of basic oxygen furnace slag (BOFS), ladle furnace slag (LFS), and ground granulated blast furnace slag (GGBFS) are studied.•Multiple tests are performed to ...determine the feasibility of these slags as SCMs.•GGBFS shows the best performance; BOFS and LFS should not be used as SCMs as-is.•The combined use of test methods is more accurate.
Limited applications for the large amounts of steel slags produced globally exist. In this study, the hydraulic and pozzolanic behavior of basic oxygen furnace slag (BOFS) and ladle furnace slag (LFS) are studied and contrasted with the behavior of ground granulated blast furnace slag (GGBFS). Pozzolanic test, isothermal calorimetry, thermogravimetric analysis, and compressive strength test are performed to determine the feasibility of these slags as supplementary cementitious materials (SCMs). The pozzolanic test is performed by measuring the heat release and calcium hydroxide consumption of slag-calcium hydroxide blends at 50 °C and pH 13.5. The other tests are performed on cementitious pastes with 20% slag replacement by mass at 23 °C and 50 °C. GGBFS shows the best performance among all slags in the tests, followed by BOFS, followed by LFS. It is suggested that BOFS and LFS should not be used as SCMs as-is. The poor performance of LFS is due to flash setting, likely caused due to the rapid reaction of C12A7, which causes hydration retardation and poor strength gain. The BOFS shows moderate performance as it has low hydraulic activity, likely explained by its low amorphous content and the presence of low amount of reactive crystalline phases. An important finding from this study is that in order to state whether materials could be used as SCMs or not, the combined use of pozzolanic test, isothermal calorimetry, and compressive strength test is more accurate than the use of only one test method. While the results obtained may here not be broadly generalizable to other materials due to variations in slag chemistry, the approach suggested may be generalizable to obtain insights into whether any powder may be used as SCM.
Identification and rapid characterization of novel supplementary cementitious materials (SCMs) is a critical need, driven by shortfalls in conventional SCMs. In this study, we present a discussion of ...recently developed reactivity tests – the R3 test, the modified R3 test, the lime strength test, and the bulk resistivity index test. These tests measure reactivity parameters such as heat release, bound water, calcium hydroxide consumption, strength, and bulk resistivity. All tests can screen inert from reactive materials. To additionally differentiate pozzolanic and latent hydraulic materials, two parameters, for example, calcium hydroxide consumption and heat release, are needed. The influences of SCM bulk chemistry, amorphous content, and fineness on measured reactivity are outlined. Reactivity test outputs can predict strength and durability of cement paste/mortar/concrete; however, caution must be exercised as these properties are influenced by a variety of other factors independent of reactivity. Thoughts are provided on using reactivity tests to screen materials for concrete durability.
Massive amounts of quarry fines are available worldwide. These materials are generally inert, thus limiting their applications. At the same time, shortfalls in conventional supplementary cementitious ...materials (SCMs) have become an increasing challenge. We can extend SCM usage and reduce filler landfilling by blending these materials together. This paper investigated the proportions of fly ash and pumice that could be replaced with inert basaltic fines without degrading properties significantly. Blended SCM reactivity, and cement paste compressive strength, bulk resistivity, and calcium hydroxide content over 91 days, and alkali-silica reaction mitigation in mortars were investigated. No/minimal synergistic effects between basaltic fines and fly ash or pumice were found. Thus, by measuring initial reactivity or bulk resistivity of end members, an estimate of reactivity, resistivity, and the effects of the blended SCMs on concrete can be established. Replacement of fly ash or pumice by inert materials is likely limited to 40%, depending on the specific applications.
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).
The dissolution kinetics of metakaolin are examined at room temperature in NaOH solutions at concentrations of (0.1, 5, or 10) mol L
−1
and at liquid-to-solid mass ratios (
L
/
S
) of 50 or 1000. ...Both the dissolved Si and Al concentrations as well as the morphology and structure of the solid are reported at various times. The dissolution rate is approximately constant for about an hour, (0.0043–0.1030) µmol m
−2
s
−1
, depending on alkalinity and
L
/
S
. Some precipitates are observed within the first ten minutes but do not affect the dissolution rate during that first hour, implying that the precipitates form in the solution and do not block or alter the metakaolin surfaces significantly. The dissolution rate during the first 45 min increases with alkalinity and decreases with
L
/
S
. The metakaolin exfoliates at higher NaOH concentrations, exposing more surface area to the solution. The effect of exfoliation increases the apparent dissolution rate and promotes more congruent dissolution. These observations not only improve our understanding of the metakaolin dissolution mechanisms but also provide insights into the reactivity of calcined clays that are becoming increasingly important to the sustainability of the cement and concrete industry.
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.
Advancements in service-life prediction of concrete in freeze-thaw environments are reviewed to help inform concrete design, specification, and future areas of research. Critical degree of saturation ...and the formation of calcium oxychloride are specifically reviewed due to recent research progress and the ability to model the service-life of concrete in freeze-thaw prone environments is discussed. The current theory, numerical modeling, and experimental efforts used to investigate critical degree of saturation and calcium oxychloride formation are summarized and a discussion of how critical degree of saturation and calcium oxychloride develop due to environmental exposure and transport of water or calcium chloride, resulting in expansive stresses (i.e., freezing or calcium oxychloride formation) is presented. Areas of future work are identified related to advancements in experimental and numerical techniques, improved on-site evaluation tools of concretes, and the adoption of design specifications and construction practices that ensure service-life under the reviewed degradation mechanisms.
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•Deep learning is used to predict carbonation data.•AIJ model, FEM analysis, and deep learning are compared with experimental data.•Deep learning can accurately predict carbonation results.
...Increasing costs due to failure and reconstruction highlight the importance of concrete durability research. Carbonation of concrete, which can accelerate corrosion, is one of the major deterioration mechanisms in reinforced concrete structures. Experimental data has been used to develop carbonation prediction models, however, the service life predicted from various models can differ significantly. A potential solution is the application of an artificial neural network algorithm, which simulates the human nervous system, to evaluate concrete carbonation. In this study, the possibility of applying machine learning to predict concrete carbonation behavior is evaluated. A deep learning model, which has the best learning power among various machine learning models, was applied. This model is structured such that hidden layers of hierarchical artificial neural networks are formed in several layers. Existing carbonation experimental data (water-to-cement ratio 0.55 and 0.65, temperature 20 °C, relative humidity 60%, and CO2 concentrations 5% and 20%) was predicted by using the deep learning model which was also compared with the results of two other models – AIJ model and FEM analysis. Under the test conditions, the differences in carbonation rate coefficient between experimental data and the deep learning results ranged from 0.01 mm/year to 0.10 mm/year for the different water-to-cement ratios and CO2 concentrations. These results were comparable though somewhat better than results from FEM analysis, which showed corresponding differences ranging from 0.08 mm/year to 1.04 mm/year. The results were significantly better than the AIJ model, which showed differences ranging from 0.32 mm/year to 2.34 mm/year. These preliminary results suggest that a deep learning algorithm can be used to accurately predict concrete carbonation results.
For geopolymers (usually composed of unreacted precursor and gel), the compressive strength is controlled by two factors. The first is the degree of reaction, or, equivalently, the amount of gel ...formed, including any calcium silicate hydrate gel in calcium-containing mixtures. The second factor is the gel composition, generally given by the Si/Al ratio. These two parameters are interrelated for typical silicate-activated metakaolin geopolymers. By separating out effects of Si/Al ratio and degree of reaction, this study quantitatively correlates the degree of reaction with the compressive strength of metakaolin-based geopolymers with and without calcium. Solid-state
Si nuclear magnetic resonance (NMR) aided with chemical extractions was used to determine gel amounts and composition for several geopolymer mixtures. The compressive strength was also measured for each mixture at 7 days. Both the increase of Na/Al ratio in mixtures without calcium and addition of external calcium increased the degree of reaction, and compressive strength correlated linearly (R
> 0.88) with the degree of reaction.
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.
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