Calcium Hydroxide Consumption Research Articles

Linking reactivity test outputs to properties of cementitious pastes made with supplementary cementitious materials

Recently developed reactivity tests for supplementary cementitious materials (SCMs) have shown the ability to differentiate between inert and reactive materials. Two promising SCM reactivity tests were used to study ten different SCMs. The first method involves quantifying the heat release, bound water, and calcium hydroxide consumption of SCMs in a simulated pore solution (modified R3 test), and the second method is a lime strength test that quantifies lime mortar strength development. Tests on cementitious pastes with a 20% SCM replacement level were conducted to determine heat release, calcium hydroxide content, bound water, compressive strength, and bulk resistivity for 35 days. Moderate correlations between the modified R3 heat release at 10 days and 1 day and between modified R3 heat release and bound water were shown, which suggests the possibility of reducing test duration and using bound water, instead of the heat release. The calcium hydroxide consumption measured from the modified R3 test correlates strongly with CaO content in the SCM and moderately to paste bulk resistivity at 35 days, demonstrating the fundamental importance of measuring calcium hydroxide consumption. Correlations between modified R3 heat release and bound water and most other paste properties were generally poor, presumably because of the high acceleration in the modified R3 tests. The compressive strength measured from the lime strength test showed moderate to strong correlation to heat release, calcium hydroxide content, bound water, and bulk resistivity of cementitious paste at 1–35 days. The fundamental importance of these reactivity tests is therefore clearly validated.

Experimental Study of the Combined Use of Fiber and Nano Silica Particles on the Properties of Lightweight Self Compacting Concrete

In fiber concretes, microcracks in the boundary area between the cement paste and the surface of aggregates or fibers are higher. Natural and artificial pozzolans can be used for reinforcing this area. In this research, the combination of glass fiber, zeolite, and nano silica particles were used in lightweight self-compacting concrete containing scoria. Fiber volume fractions between 0% to 1.5% in combination with 0% to 6% nano silica particles were examined. The scoria aggregates and zeolite were considered constant in all mixes. The fresh and hardened properties of specimens were evaluated using T50, slump flow, V-funnel, L-box, compressive strength, splitting tensile strength, flexural strength, ultrasonic, electrical resistivity, and water absorption tests. Also, the microstructure of concrete was investigated using scanning electron micrograph images. The combined use of nano silica particles and glass fiber increased the splitting tensile strength by about 3 to 56%. Also, the use of nano silica particles increased electrical resistivity by 136 to 194%. Nano silica particles, due to their high specific surface and high reactivity, result in consuming calcium hydroxide that is quickly organized within the hydration, filling pores of the calcium silicate gel structure and eventually producing more and more compacting hydrated products.

A fresh perspective on effect of metakaolin and limestone powder on sulfate resistance of cement-based materials

A study of metakaolin and limestone powder on sulfate resistance of cement-based materials was carried out by compressive strength changes, sulfate attack experiment as well as the microstructure development using X-ray diffraction (XRD), thermogravimetric analysis (TG/DTG), and 27Al magic-angle spinning nuclear magnetic resonance (27Al MAS NMR) techniques. It was found that metakaolin with 10% was optimum for compressive strength increase of mortars. While a dosage of 20% is required for improving sulfate resistance through significant consumption of calcium hydroxide, induction of Al into C-(A)-S-H rather than ettringite and the increase of mean chain length (MCL) of C-S-H. Limestone powder displayed certain chemical reactivity to promote the formation of thermostable product monocarboaluminate for the suppression of sulfate attack at some extent, while hybrids of metakaolin and limestone powder showed a negative sulfate resistance owing to the insufficient dosages of metakaolin within 5–10%. This study provided a constructive perspective on the using of metakaolin and limestone powder to improve sulfate resistance of cement-based materials.

Comparison of the effects that supplementary cementitious materials replacement levels have on cementitious paste properties

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.

Assessment of the ground aggregate paste (GAP) test for aggregate alkali–silica reactivity screening

This paper investigates the potential of a laboratory test for the screening of aggregate reactivity to alkali–silica reaction (ASR) through phase analysis of the phases developed in ground aggregate paste (GAP) specimens subjected to accelerated ageing. GAPs were prepared using two aggregates categorised as non-reactive and potentially reactive by standard expansion test methods and were aged at 40, 60 and 80 °C in 1 M NaOH solution over periods up to 84 days. Phase development was monitored using TG, XRD and FTIR, and the reactivity was correlated with quartz and calcium hydroxide consumption. The data demonstrate that this test has the potential to be developed as a screening test, based on the correlation of phase consumption with Australian standard expansion test reactivity categorisation.

A comparison of test methods to assess the strength potential of plain and blended supplementary cementitious materials

This paper studies the effectiveness of various test methods to measure the reactivity of combinations of supplementary cementitious materials (SCMs). While several test methods that quantify the reactivity of individual SCMs are available, the advent of ternary cements necessitates the testing of not just the individual SCMs, but also their combinations. The study was carried out on fly ash (FA), slag, calcined clay, limestone (LS) and their blends. Various standardised and non-standardised test methods, that measure the physical and chemical characteristics of SCMs were studied. The measurements from these test methods were compared to the 28-day compressive strength of cement mortars, partially replaced by the respective SCMs or their blends. It was observed that most of the test methods that are used for individual SCMs are also suitable for use with the blends of SCMs. In this way, the compatibility of the two SCMs being blended can also be tested. It was found that test methods that measure the consumption of calcium hydroxide (CH) are not suitable for testing SCMs and blends containing slag. Methods involving the measurement of heat of hydration and bound water are more suitable for such SCMs. It was also seen that the reliability of simple indirect test methods is similar to other more sophisticated test methods.

Experimental investigation on optimization of vegetation performance of porous sea sand concrete mixtures by pH adjustment

The purpose of this paper is to investigate the effect of different methods on reducing the pH value of soil in Porous Sea Sand Concrete Mixtures (PSSCM) through a series of experiments. Thereinto, the X-ray diffraction (XRD) technology was applied to analyzing the mechanism of pH value change, and the relationship between the fundamental performance (effective porosity, sound absorption coefficient and compressive strength) and the optimum mixture proportion of PSSCM successfully. In all experiments, plant varieties which have a high matching degree with PSSCM were screened out, and the vegetation performance of PSSCM was verified by field investigation. Consequently, it is showed that the content of calcium hydroxide in PSSCM was positively correlated with the pH value of soil in PSSCM. The four approaches, adding mineral admixtures, appending acid-modified materials, accelerating carbonization, and immersing Deep penetration sealer (DPS), help reduce the pH value. Among them, the lowest pH value (7.8) was obtained by the addition of 10% silica fume, accelerating carbonization for 28 days, and subsequently immersing in DPS for 28 h. Besides, these methods all reduce PSSCM pore and soil pH value by consuming calcium hydroxide. In addition, the best fundamental performance was obtained on the condition that the water-cement ratio of PSSCM was 0.26 and the effective porosity of PSSCM was 25.95%. Likewise, the matching degree between tall fescue and PSSCM was the best under this pH condition. After 120 days of sowing, their stems were thick and strong, and leaves were green and lush. In the meantime, their rhizomes length exceeds 8 cm.

Instant CO2 curing for dry-mix pressed cement pastes: Consideration of CO2 concentrations coupled with further water curing

Early-age carbonation can make a significant difference in the formation of hydration products in cement-based materials and alter the microstructural and mechanical performances. To understand in detail the impacts and their contribution to cement hydration, dry-mix cement pastes were exposed to instant carbonation with 0.04 %, 1%, 3%, 10 %, 20 % CO2 concentrations for 2 h prior to further water curing. By increasing the CO2 concentration, an increment in strength gain of samples at 2 h (right after early carbonation) as well as being prolonged by water curing at 1, 3, 7 days was noticed. This agrees with TGA and XRD results, demonstrating that the increases in CO2 concentration resulted in a higher carbonation reaction and hydration degree. 29Si NMR results also indicate that the higher the CO2 concentration the lower the calcium to silica ratio (Ca/Si); thus, there is a higher degree of polymerization to promote early hydration. It can be concluded that early carbonation of 2 h in particular with a high CO2 concentration can be beneficial for further cement hydration due to the consumption of calcium hydroxide (CH) and nuclei site effect of calcite crystals, resulting in better microstructural properties and mechanical performance.

MICROSTRUCTURAL AND PHYSICAL CHARACTERIZATION OF SOLID WASTES FROM CLAY BRICKS FOR REUSE WITH CEMENT

This study aims to evaluate the properties of different wastes obtained from four red ceramic brick industries in the northern region of Santa Catarina, Brazil. The characterization of the clay brick waste (CBW) was performed using the XRD techniques, XRF, FTIR, DTA and SEM. Techniques to determine the pozzolanic activity, particle size, B.E.T. surface area and specific mass were used. The consumption of calcium hydroxide (CH) in the cementitious pastes with the CBWs was also measured. An application in mortar is also analysed. The results indicated that the CH consumption was a function of the large surface area of the waste particles. The CBW reactivity is favoured by firing temperature adequate (about 800 C), low presence of K2O and impurities and higher kaolinite content. CBW-B showed the highest consumption of calcium hydroxide in the cement pastes tested (remaining 0.40% CH). Morphological analysis showed that microcrystals of halloysite was smaller than those of kaolinite and have more elongated profile. These differences provide the larger surface area observed for halloysite and this has an influence on the reactivity. The reference paste presented CH content of 2.37%. The compressive strength of the mortar with CBW improved comparing to reference, in 28 days (from 2.45 to 5.65 MPa), and in 90 days (from 5.72 to 10.39 MPa). The use of these wastes could reduce solid waste discards in many regions. Besides reducing CO2 emissions and saving natural resources from the manufacture of cement.

Effect of Nanosilica on Impermeability of Cement‐Fly Ash System

Surface protection has been accepted as an effective way to improve the durability of concrete. In this study, nanosilica (NS) was used to improve the impermeability of cement‐fly ash system and this kind of material was expected to be applied as surface protection material (SPM) for concrete. Binders composed of 70% cement and 30% fly ash (FA) were designed and nanosilica (NS, 0–4% of the binder) was added. Pore structure of the paste samples was evaluated by MIP and the fractal dimension of the pore structure was also discussed. Hydrates were investigated by XRD, SEM, and TG; the microstructure of hydrates was analyzed with SEM‐EDS. The results showed that in the C‐FA‐NS system, NS accelerated the whole hydration of the cement‐FA system. Cement hydration was accelerated by adding NS, and probably, the pozzolanic reaction of FA was slightly hastened because NS not only consumed calcium hydroxide by the pozzolanic reaction to induce the cement hydration but also acted as nucleation seed to induce the formation of C‐S‐H gel. NS obviously refined the pore structure, increased the complexity of the pore structure, and improved the microstructure, thereby significantly improving the impermeability of the cement‐FA system. This kind of materials would be expected to be used as SPM; the interface performance between SPM and matrix, such as shrinkage and bond strength, and how to cast it onto the surface of matrix should be carefully considered.

Ceramsite vegetated concrete with water and fertilizer conservation and light weight: Effect of w/c and fertilizer on basic physical performances of concrete and physiological characteristics of festuca arundinacea

In this study, vegetated concrete is prepared with ceramsite as aggregate, and urea and diammonium hydrogen phosphate (DAP) as fertilizer to treat soil and water loss in ecologically-imbalanced slopes. The effects of water-cement ratio (w/c) and fertilizer on these properties are studied. The results demonstrate that the w/c causes compressive strength and porosity to increase and then decrease. When the w/c is 0.25, the 28-day compressive strength and connected porosity reach the highest values of 5.69 MPa and 33.66%, respectively. When exposure time reaches 240 h, the water release rate with the w/c of 0.25 is the lowest, at 79.02%. The dry density remains at approximately 708 kg/m3. Urea causes the compressive strength, porosity, and water permeation coefficient to rise slightly, and the alkalinity to reduce sharply. As urea increases the paste porosity by inhibiting ettringite formation and consuming calcium hydroxide crystals, the 56-day total nitrogen (TN) cumulative release rate is 86.12% with 3.5 wt% urea. DAP is not suitable as fertilizer in vegetated concrete, because the PO43- from DAP dissolution can react with Ca2+ and Mg2+ from the cement to generate a phosphate precipitate. The 56-day total phosphorus (TP) cumulative release rate is only 0.25%, with 3.5 wt% DAP.

Influence of Silica Fume Additive and Temperature History on the Volume Change of Ultra-High-Strength Cement Paste and Concrete

Abstract In this article, the temperature dependency of the autogenous shrinkage and the thermal expansion coefficient (TEC) of ultra-high-strength concrete (UHSC) and cement paste is discussed. The concrete and cement paste binder is mixed with portland cement and silica fume (SF) with water-to-binder ratios ranging from 13 to 20 % and SF replacement rates ranging from 7.5 to 17.5 %. First, we confirm that the autogenous shrinkage of a concrete specimen can be estimated from that of cement paste by using the theory of composite materials. Second, the SF reaction ratio and portlandite consumption for each temperature history is examined simultaneously with measurements of the autogenous shrinkage and the TEC of ultra-high-strength cement paste. The results show that, for the same specimen, the apparent activation energy of autogenous shrinkage and TEC is larger than that of physical properties such as Young’s modulus. This is attributed to the amount of calcium hydroxide consumption per SF reaction being much larger at high temperatures than at 20°C and the rapid increase in the Brunauer-Emmett-Teller (BET)-specific surface area of hardened cement paste at high temperatures. From the previous results, it is inferred that the microstructure of UHSC containing SF is modified to exhibit increased sensitivity to volume. These results indicate that not only the thermal strain but also the thermos-active properties of autogenous shrinkage need to be considered when conducting numerical analysis for crack risk assessment.

Mechanical properties and microstructure of ultra-high performance cement-based composite incorporating RHA

The effects of the addition of rice husk ash (RHA) on the mechanical and microstructural properties of an ultra-high performance cement-based composite (UHPCC) was studied. The microstructure of the UHPCC was investigated using X-ray diffraction, mercury intrusion porosimetry, scanning electron microscopy and other analytical test methods. The results showed that the mechanical performance was improved with the addition of RHA. Mortars blended with 15% RHA showed the highest compressive and flexural strengths. For mortars reinforced with 3% steel fibres by volume, both flexural and compressive strengths were remarkably enhanced. The optimal content of RHA was found to be about 10–15%. The addition of RHA decreased the hydration heat evolution rate of the cementitious composites, but the hydration process was brought forward due to the addition of RHA. As a result of calcium hydroxide consumption through the pozzolanic reaction of the RHA, the interface was strengthened with an increase in curing time and the microstructure of the mortar containing RHA blended was denser than that of mortar without RHA. The high pozzolanic reaction and the filler effect of RHA contributed to a finer pore structure and a decrease in porosity.

Autogenous Shrinkage, Pozzolanic Activity and Mechanical Properties of Metakaolin Blended Cementitious Materials

In the literature, there are some conflicting results regarding the influence of metakaolin (MK) addition on autogenous shrinkage behavior of cementitious materials. In this study, with the aim of identifying how the use of MK changes the properties of cementitious materials, cement was partially replaced by MK in different proportions (8%, 16%, and 24%) in pastes produced with variable water/binder ratios (w/b; 0.28, 0.35 and 0.42). The temperature development and calcium hydroxide consumption by thermogravimetric analysis were observed to better characterize the effects of MK on the autogenous shrinkage behavior. The mechanical properties such as compressive strength and flexural strength were experimentally investigated. The results show that the addition of MK has contrasting effects on autogenous shrinkage during early ages depending on the w/b ratio. Thermogravimetric analysis showed that the amount of stratlingite was smaller in pastes with low w/b ratios than in pastes with high w/b ratio. The calcium hydroxide consumption with the pozzolanic reaction of MK was significant even at 2 days, but consumption ratios with respect to the reference paste slowed down at 7 to 28 days.

Experimental study of the effect of nano-additives on the stiffness of cemented fine sand

ABSTRACT The stiffness of stabilized sand with powder nanomaterials (nano-SiO2, nano-Al2O3, and nano-MgO) in two cementation conditions is investigated in this study. The studies have been conducted using laboratory tests under unconfined, partly confined, and confined conditions. The nanomaterials in addition to filling the intergranular pore spaces have led to a better interlocking of the particles by improving the concentration on the surface roughness of them in an effective way. Therefore, they have increased the intergranular friction, resisted the movements of the particles, and reduced the deformation of the mass. In the cemented case, nanomaterials have generally participated in the hydrated medium of the cementitious matrix. In addition, pozzolanic materials have reduced the weak part of the hydration process and improved the strong part of it, by consuming calcium hydroxide and producing C-S-H. Subsequently, it has resulted in a reduction of axial and volumetric deformation of the specimens..

Effect of Fineness of Basaltic Volcanic Ash on Pozzolanic Reactivity, ASR Expansion and Drying Shrinkage of Blended Cement Mortars.

This study focuses on evaluating the effect of the fineness of basaltic volcanic ash (VA) on the engineering properties of cement pozzolan mixtures. In this study, VA of two different fineness, i.e., VA fine (VF) and VA ultra-fine (VUF) and commercially available fly ash (FA) was used to partially replace cement. Including a control and a hybrid mix (10% each of VUF and FA), eleven mortar mixes were prepared with various percentages of VA and FA (10%, 20% and 30%) to partially replace cement. First, material characterization was performed by using X-ray florescence (XRF), X-ray powder diffraction (XRD), particle size analysis, and a modified Chappelle test. Then, the compressive strength development, alkali silica reactivity (ASR), and drying shrinkage of all mortar mixes were investigated. Finally, XRD analysis on paste samples of all mixes was performed to assess their pozzolanic reactivity at ages of 7 and 91 days. The results showed increased Chappelle reactivity values with an increase in the fineness of the VA. Mortars containing high percentages of VUF (20% and 30%) showed almost equal compressive strength compared to corresponding FA mortars at all ages, however, the hybrid mix (10% VUF + 10% FA) exhibited higher strength than that of the reference mix (100% cement), particularly, at 91 days. At low percentages (10%), ASR expansion in both VF and VUF mortars was higher compared to the corresponding FA mortar and the opposite behavior was observed at high percentages (20% and 30%). Among all the mixes including the control, mortar with VUF was found to be most effective in controlling drying shrinkages at all ages. The rate of consumption of calcium hydroxide (Ca(OH)2) for pastes containing VUF and FA was almost the same, while VF showed low Ca(OH)2 intensity. These results indicate that an increase in the fineness of VA significantly improvs performance, and therefore, it could be a feasible substitute for commercial admixtures in cement composites.

Investigating the pozzolanic reaction of post-consumption glass powder and the role of portlandite in the formation of sodium-rich C-S-H

The use of glass powder (GP) as an alternative SCM offers a viable opportunity to partially substitute OPC, and therefore provides economic and environmental benefits. Moreover, the predominant siliceous amorphous phase provides the required component for its use as pozzolanic material. In this work, the mechanism and the products of the finely ground GP reaction with lime are investigated. The released silica, from glass dissolution, reacts with calcium hydroxide (CH) to form C-(N)-S-H with different compositions depending on the system. In the studied CH-GP binder systems, the fineness of GP ensures a higher surface for silica to react, leaving time for the pozzolanic reaction to take place. However, the glass continues to react even after the consumption of CH, which may lead to the apparition of alkali-silica gels around the particles in the long term.

The failure process of mortars during sulfate attack

External sulfate attacks on concrete structures may cause serious damage and it has attracted a wide range of attention from numerous researchers over the past decades. However, many studies have been concentrated on the sample which has been already destroyed. This paper investigated the entire deterioration process of mortars that were immersed in Na2SO4 solution containing 3 gSO4 2-/L and 33.8g SO4 2-/l at 20 o C up to 600 days. The study on time-varying regularity of expansion, cracks, compressive strength and mineral phases was investigated. Back scattered electron image was used to further examine the evolution of microstructures of the mortars during the attack process. The results showed that damage process of mortars can be described as induction stage, surface damage, bulk damage and then completely damage stage. Fine ettringites that were formed in restricted spaces, approximately 2-5 μm, result in surface damage. At the bulk damage stage, cracking was the main characteristic of mortar which leads to obvious expansion. In this stage, some large ettringite crystals (>20μm) were just deposited in the formed cracks. At the later stage, gypsum can be easily formed at interfacial transition zones as the consumption of calcium hydroxide, which mainly contributed to completely strength failure rather than expansion.

New insights from reactivity testing of supplementary cementitious materials

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).

Hydration and strength development in blended cement with ultrafine granulated copper slag.

This study aims at evaluating the effect of ultrafine granulated copper slag (UGCS) on hydration development of blended cement and mechanical properties of mortars. The UGCS with the median particle size of 4.78 μm and BET surface area of 1.31 m2/g was used as a cement replacement to prepare blended cements. Hydration heat emission of blended cement and mechanical performance of mortars were investigated by using isothermal calorimetry and strength tests, respectively. X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) were applied to the analysis of pozzolanic reaction and hydration products. The results illustrate that UGCS has influence on the hydration heat evolution of blended cement due to its filler effect and pozzolanic reaction. The cumulative hydration heat of blended cement is reduced by partial cement replacement with UGCS. The test mortar prepared by using blended cements with 30 wt. % UGCS shows a retardation of strength development with a low value at early ages (7 days) and a rapid growth at later ages (28 days). The 90-day compressive strength of test mortar is 45.0 MPa close to that of the control mortar (49.5 MPa). The obtained results from XRD and TGA analysis exhibit an increase in calcium hydroxide (CH) consumption and calcium silicate hydrates (C–S–H) formation in blended cement pastes with curing time. The cement replacement with UGCS induces changes in microstructure of blended cement paste and chemical composition of hydration products.