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Heat evolution of optimized blended cement pastes. a Rate of heat evolution and b cumulative heat of hydration
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To optimize the hydration process of blended cement, cement clinker and supplementary cementitious materials (SCMs) were ground
and classified into several fractions. Early hydration process of each cementitious materials fraction was investigated by
isothermal calorimeter. The results show fine cement clinker fractions show very high hydration rat...
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... The model of isothermal calorimeter was Calmetrix I-CAL 800 HPC. Heat evolution measurements were collected from the time of mixing until 72 h since the slow rate of heat evolution of blended cement and SCMs mixtures [57,58]. ...
... The influence of SAP on the hydration process and setting time is mainly attributed to the change in internal water content and alkali ion concentration caused by the additional water. High alkali concentration (high pH) in the pore fluid can accelerate the hydration progress [38,39]. When SAP is added without the additional water, the flowability of UHSM is dramatically reduced. ...
Employing CaO-based expansive agent (CaO-based EA) and superabsorbent polymer (SAP) in ultra-high performance concrete (UHPC) is a effective strategy to mitigate the shrinkage. The cracking identification can help to verify whether the cracking risk can be reduced. In this paper, the shrinkage cracking behavior of ultra-high strength mortar (UHSM, UHPC matrix) with different dosage of CaO-based EA and SAP was observed based on the temperature stress testing machine (TSTM) tests. The coupling mechanism of EA and SAP was investigated by comparing the cracking process to hydration progress, hydration product and internal water distribution at each stage. Furthermore, the creep and elastic modulus were also calculated to clarify the cracking risk development of UHSM with EA and SAP. Unlike ordinary concrete, “Time-zero” of shrinkage should also be redefined in UHSM
with EA and SAP due to the change in early age deformation rate. Although the addition of EA and SAP can significantly increase the expansive deformation of UHSM at early age, cracking still occurs due to the post-peak shrinkage.
... The reason can be attributed to the change of alkali concentrations in pore solutions. With the increase of w/c, the initial alkali ion concentration of pore solution is reduced and results in the retardation of the second exothermic peak [53,54]. The third exothermic peak is generally ascribed to the renewed reactivity of the aluminate phases, due to the depletion of gypsum as reported in Ref. [55]. ...
This paper presented a comprehensive study on the early-age hydration process and autogenous shrinkage evolution of high performance cement (HPC) pastes based on ¹H nuclear magnetic resonance relaxometry (¹H NMR). The transverse relaxation time (T2) was measured to characterize the water consumption process of cement pastes. The hydration process and hydration degree of HPC pastes were contrastively analyzed by using ¹H NMR, isothermal calorimetry, and thermogravimetry analyses (TGA). Results showed that the initial setting time was the onset that free water signal fraction started to drop, and after this moment, the hydration rate of cement was increased and more hydration products were generated. A magnetism-heat (M-H) model was established to characterize the early-age hydration process and microstructure evolution of HPC pastes according to the relationship between free water consumption rate and hydration exothermic rate. The hydration degree of cement calculated by ¹H NMR and TGA showed good agreement, with the error of α values less than 2% after initial setting. Furthermore, the free water consumption process had a good correlation with the development process of autogenous shrinkage for HPC pastes with different water to cement ratio.
... However, as observed in this study, the hydration retardation effect of CNF is dependent on the w/c. For pure cement paste, an increase in w/c decreases the rate of heat release at the early stage of hydration [42,43]. As reported by Justs et al. [42], an increase in w/c of cement paste makes the pore solution diluted with respect to alkalis and hydroxyl ions which provides less acceleration of the cement hydration and hence, results in lower heat release. ...
This article presents a comprehensive investigation on the effects of pure cellulose nanofibrils (CNF) and nanosilica containing CNF on the performance of ordinary portland cement (OPC) paste. The effects of CNFs on cement paste rheology, hydration, microscopic phase formation, compressive strength, and fracture parameters were monitored. Sol-gel method was used to synthesis nanosilica particles within CNF slurry. The effects of CNF on cement hydration was found to be dependent on the water to cement ratio (w/c). Specifically, CNFs accelerated the early age cement hydration at 0.35 w/c, but this acceleration effect was not prominent for 0.45 w/c. Such w/c dependent effect was attributed to the negatively charged hydroxyl and carboxyl surface sites of CNFs which can bind alkali ions or cement particles. The concentration of alkali ions in cement pore solution depends on the w/c and hence, resulting the w/c dependent effects of CNF. The colloidal stability of CNF was found to improve due to the addition of nanosilica particles. Addition of CNF was found to increase the flexural strength of cement paste up to 75%. The effects of CNF addition on the compressive strength of cement paste matrix was negligible.
... The higher amount of reactants from the activator and the longer acceleration period contribute to the higher total heat release of mixtures with higher l/b without SAP ( Fig. 4(b)). The delayed appearance of the main reaction peak and the increased total reaction degree of the paste with higher l/b are similar to what has been reported for OPC paste [63][64][65]. ...
In this study, internal curing by superabsorbent polymers (SAP) is utilized to mitigate self-desiccation and au-togenous shrinkage of alkali-activated slag (AAS) pastes. Absorption and desorption kinetics of SAP incorporated in AAS pastes were studied with X-ray tomography. Internal curing delayed the peak of the rate of heat liberation but increased the total reaction degree of AAS pastes. Internal curing by SAP mitigated effectively the drop of internal relative humidity and the self-desiccation-induced autogenous shrinkage of AAS pastes. The cracking tendency of AAS pastes undergoing shrinkage in restrained conditions was also significantly reduced with SAP. Nonetheless, adding SAP, regardless of their content, cannot eliminate the autogenous shrinkage of AAS pastes, suggesting the existence of other autogenous shrinkage mechanism(s) besides self-desiccation.
... Since ultrafine Portland cement and ultrafine GBFS were used, the PC-GBFS pastes had high hydration degree after 28 days curing (>85%) according to previous investigation [32], then hydration products were characterized to clarify the influence of GBFS. ...
An optimization of Portland cement (PC)-supplementary cementitious materials (SCMs) system focusing on the characteristics of hydration products is significantly important to decrease the thermal and chemical shrinkages and increase the chloride binding capacity, consequently to decline the diffusion rate of chloride into cement-based materials. In the present study, ultrafine granulated blast furnace slag (GBFS) was added into ultrafine Portland cement (PC) pastes to obtain homogenous hydration products, and then the hydration heat, chemical shrinkage, chloride binding capacity and stability of the PC-GBFS pastes were investigated. The results show that with the increase of the GBFS addition, the ultimate hydration heat of the PC-GBFS pastes increased initially and then decreased sharply, and the chemical shrinkage increased slightly with the increase of the GBFS addition. The cement pastes with 40–60% GBFS had acceptable hydration heat and chemical shrinkage, more important, its total bound chloride and non-water-soluble bound chloride increased by 24% and 177%, respectively, compared to those of Portland cement paste. Additionally, about 50% of chemically bound chloride in the form of Friedel’s salt was water-soluble chloride due to ion-exchange, and 5–20% of physically bound chloride in C-S-H was non-water-soluble chloride after desorption.
... An important parameter that paves the way for improved slag reutilization is the type of binder material used [62]. Other factors that affect composite material performance involve initial factors such as chemical composition and specified preparation parameters such as water-binder ratio, drying shrinkage, etc., which are directly affected by the fineness of initial materials used [63]. Reportedly, increasing fineness of initial material particles also increase their affinity to react with water which in turn provides improved short term compressive strength of the cement produced as a result of reduced porosity [64]. ...
Ever-increasing energy costs and environmental restrictions have compelled researchers to focus on the reutilization of vast amounts of industrial by-products such as blast furnace slag and steelmaking slag, in energy extensive and material extensive industries such as iron-steel production and construction. Attempts to reutilize these waste materials all around the world have yielded successful results up to date, such that, in some of these attempts they even surpassed their intended use as blend or replacement materials and became serious rivals to their industrial counterparts. Various ways to reutilize these waste materials have been explored up to date, including waste heat recovery, clinker substitute in cement production, and a number of comparatively more value added applications. The ongoing attempts have come to a point that pushes the limits for more technological uses such as alternative ceramic coating materials in surface engineering applications. In this regard, this review study aims to provide an overview of and a collective approach to various uses of blast furnace and steelmaking slag in diverse applications and fields, with a view to provide insight into the current attempts to optimize or improve their use, as well as emerging trends as to the potential use of these waste materials in higher value-added applications.
... Metakaolin has pozzolanic properties (Frías et al. 2000;Sha and Pereira 2001;Gartner 2004;Nadeem et al. 2013). It is more reactive than silica fumes, which are in turn more reactive than slags (Largent 1978;Zhang et al. 2012;Palou et al. 2016). Water is required to activate the pozzolanic activity (Wild et al. 1996), which may weaken the mechanical strength of the material (Boháč et al. 2016). ...
Polluted soils are a serious environmental risk worldwide and consist of millions of tons of mineral waste to be treated. In order to ensure their sustainable management, various remediation options must be considered. Hydraulic binder treatment is one option that may allow a stabilisation of pollution and thus offer a valorisation as secondary raw materials rather than considering them as waste. In this study, we focused on sulphate-polluted soil and tested the effectiveness of several experimental hydraulic binders. The aim was to transform gypsum into ettringite, a much less soluble sulphate, and therefore to restrict the potential for sulphate pollutant release. The environmental assessment of five formulations using hydraulic binders was compared to the gypsiferous soil before treatment (contaminated in sulphate). The approach was to combine leaching tests with mineralogical quantifications using among others thermogravimetric and XRD methods. In the original soil and in the five formulations, leaching tests indicate sulphate release above environmental standards. However, hydraulic binders promote ettringite formation, as well as a gypsum content reduction as observed by SEM. The stabilisation of sulphates is, however, insufficient, probably as a result of the very high content of gypsum in the unusual soil used. The mineralogical reactions highlighted during the hydration of hydraulic binders are promising; they could pave the way for the development of new industrial mixtures that would have a positive environmental impact by allowing reuse of soils that would otherwise be classified as waste.
... In Fig. 6(a), as the LWS content was increased from 0 to 50%, the primary peak of hydration heat flow is shifted to a later time, indicating that the use of LWS retarded the early-age hydration. The retardation of the primary peak of hydration heat flow can be attributed to the released internal curing water and increased space for nucleation, due to the addition of LWS [3,29]. As expected, the retarded hydration of the mixtures with LWS led to delay in initial and final settings ( Table 3). ...
In this study, 0 to 75% volume of river sand was replaced by an equivalent amount of pre-saturated lightweight sand (LWS) to enhance mechanical properties and reduce autogenous shrinkage of ultra-high-performance concrete (UHPC). The use of LWS is demonstrated to effectively decelerate and reduce the drop in internal relative humidity and autogenous shrinkage of UHPC. Isothermal calorimetry and thermal gravimetry results showed that the use of LWS promoted cement hydration degree after 28 d of hydration. Mercury intrusion porosimetry and scanning electron microscope analyses revealed that the porosity was decreased and interface properties between sand and cement matrix is enhanced by use of LWS up to 25%. The optimum replacement ratio of LWS to river sand was found to be 25%, which resulted in the highest compressive strength (168 MPa at 91 d), flexural strength (24 MPa at 28 d), and autogenous shrinkage limited to 365 μm/m at 28 d.
... In addition, the CaO in GGBF slag can create C-S-H from a hydration reaction similar to OPC but at a very slow rate [9]. The heat evolution of Portland cement pastes containing pozzolanic material or GGBF slag was measured using an isothermal conduction calorimeter at constant temperature in order to study the early hydration [10,11]. ...
... The cumulative heat evolution and the replacement of cement by GGBF slag with different particle sizes at 24 and 72 h is illustrated in Fig. 8. The figures show that the cumulative heat evolution of the small particle size and large particle sizes of GGBF pastes are slightly different at 24 h. a b c Fig. 7. Cumulative heat evolution of GGBF pastes with different particle sizes: a -50 % replacement of OPC; b -60% replacement of OPC; c -70% replacement of OPC a b of paste containing GGBF slag increased with the increased of GGBF slag fineness [10]. For example, LGGBF50 paste had a cumulative heat evolution of 115.8 J/g at 24 h, and it increased to186.6 ...
This paper investigated the heat evolution of pastes containing inert and active materials with different particle sizes. Ground river sand was used as an inert material while ground granulated blast furnace (GGBF) slag was used as an active material. Ground river sand (GRS) and GGBF slag were ground to have the same particle size and were used separately as a replacement of Portland cement type I at rates of 50 - 70 % by weight of the binder. Heat evolution of pastes containing GRS and GGBF slag was measured using an isothermal conduction calorimeter up to 72 h. The results showed that GRS with different particle sizes had a slight effect on the heat evolution of pastes. GGBF slag with median particle size d50 of 4.4 µm and d50 of 17.8 µm had a small effect on the heat evolution of pastes during the first 24 h, and the pastes also had very low heat evolution for up to 72 h. At the same replacement rate of Portland cement, however, the heat evolution due to the slag reaction was slightly increased when the particle size of the GGBF slag was decreased. Finally, the higher is the cement replacement by GGBF slag, the higher is the slag reaction. © 2017, Kauno Technologijos Universitetas. All rights reserved.
