Rate Of Heat Evolution Research Articles

Reaction kinetics and microstructure of pegmatite‐based geopolymer composites: influence of calcined clay nature

AbstractThis research reports the investigations of threshold reactivity limit of blends of pegmatite with different calcined clays as well as the influence of calcined clay source on the geopolymerization kinetic, microstructural, and physico‐mechanical properties of feldspathic mineral‐based inorganic polymer composites. These composites were designed from 85 to 94 wt% of the solid solution of pegmatite and calcined clay. The three‐point flexural and compressive strengths, porosity, and microstructure as well as heat evolution rate of geopolymerization reactions of resulting composites were affected by the type of calcined clay. The four calcined clays provided the highest mechanical properties of the composites when added in the range of 12–15 wt%. Specifically, the values of flexural and compressive strengths ranged from 32 to 34 MPa and 101 to 105 MPa, respectively, for geopolymer composites with 15 wt% of metakolin added, while they ranged from 38 to 42 MPa and 106 to 107 MPa with 12 wt% of meta‐hallosyte added. The polycondensation/polymerization process of calcined clay developed sufficient amounts of N‐A‐S‐H and polysialate geopolymer to cover the incongruently dissolved fine particles of pegmatite. The resulting microstructure was dense and compact with the lower cumulative pore volume at about 91 mm3/g. It was concluded that designing the pegmatite/clay‐based geopolymer composites with high mechanical strengths and low porosity resulted in sustainable, low energy consumption and environmental‐friendly materials for civil engineering.

Reaction kinetics and properties of pumice-based geopolymer systems cured at room temperature

This research investigated the kinetics of pumice-based geopolymer systems and their physical and mechanical properties. The effect of the Na2SiO3/NaOH ratio of geopolymer systems on the rate of heat evolution and total heat of reaction were examined via isothermal calorimetry of geopolymer pastes prepared with Na2SiO3/NaOH ratios of 2.5, 3, and 3.5. Hardened pastes were also studied with thermo-gravimetric analysis to determine weight loss. In addition, the unit weights and compressive strengths of the pastes prepared using pumice were measured. Although the hydration process starts the earliest in pumice-based geopolymer pastes with a Na2SiO3/NaOH ratio of 2, they have the lowest total hydration temperature. Na2SiO3/NaOH ratio of 2.5 by mass, shows higher weight loss obtained from TGA results. The compressive strength of the paste sample, prepared with a Na2SiO3/NaOH ratio of 3.5 by mass, was the highest, with 36.30 MPa at 28d. Depending on the Na2SiO3/NaOH ratio, it is thought that as the amount of Na2SiO3 increases in the samples, silica gel formation increases in later ages.

Role of Glucose as Retarding Agent of Magnesium Phosphate Cement

Magnesium phosphate cements (MPCs) find application as alternative inorganic binders in construction, for crack repair and recycling of hazardous wastes. For the most common formulation, setting occurs through the reaction in water between magnesium oxide and potassium dihydrogen phosphate. The products include MgKPO4·6H2O (MKP) and an amorphous phase. Their use is somehow limited by the short working time and excessive release of heat. In this work, glucose has been introduced in the formulation of MPC to extend the setting time and modulate the rate of heat evolution. This can be considered an inexpensive and sustainable solution. The mechanism of action of the additive has been studied by investigating the reaction with isothermal conduction calorimetry, whereas the microstructure and phase composition of the obtained cements have been studied with scanning electron microscopy and X-ray powder diffraction, respectively. Results indicated that the additive influenced the reaction path thanks to the interaction at the molecular level with the dissolution process of magnesium oxide, as well as with the nucleation and growth of MKP. This has been confirmed by the changes induced in the size and shape of MKP crystals observed after the experiments conducted on diluted systems.

Influence of Copper and Zinc Tailing Powder on the Hydration of Composite Cementitious Materials.

Copper and zinc tailing powder (CZTP) is finely ground waste after copper minerals and zinc minerals have been extracted from ores during beneficiation. CZTP has certain potential cementitious properties and can be used in composite cementitious materials. The pore size distribution and hydrate phase assemblage of the hardened samples are investigated using MIP and XRD. SEM is employed to examine the microstructure of the specimens. The chemically bonded water is used to measure the degree of hydration. CZTP lowers the hydration heat evolution rate and the total hydration heat. The hydration heat evolution rate reduces as the w/b ratio rises, whereas the total hydration heat of blended cement paste rises. CZTP diminishes the strength development of the Portland-CZTP system, and the strength decreases as the CZTP level increases. CZTP reduces the critical pore diameters of the Portland-CZTP system with w/b = 0.3 after curing for 3 d and 28 d, while increasing the critical pore diameters of samples with w/b = 0.45 at the same age. CZTP increases the gel micropores of Portland-CZTP. Although CZTP increases the pore volume content of blended cement pastes with w/b = 0.3, the volume of harmful pores decreases. The pore volume content of the Portland-CZTP system decreases as the w/b ratio increases. However, the volume of harmful pores increases with a higher w/b ratio. The main hydration products in the Portland-CZTP system are portlandite, ettringite, and C-S-H. CZTP mainly played the role of filling or acting as a microaggregate in the Portland-CZTP system.

Influence of metakaolin and calcined montmorillonite on the hydration of calcium sulphoaluminate cement

Calcium sulfoaluminate (CSA) cement-calcined clay blends have shown great potential as new lower CO2 footprint cementitious materials. The influences of metakaolin and calcined montmorillonite on the hydration of CSA cement were studied from aspects of setting time, physical strength and drying shrinkage, while fly ash was chosen for comparison. Meanwhile, hydration heat evolution and the microstructure of hydrates of modified CSA cement paste at early age were determined by means of calorimetry, XRD, SEM and DTA-TG. Results show that both metakaolin and calcined montmorillonite do not contribute to the formation of new kinds of hydrates. They shorten the setting time and reduce the strength, while effectively reduce the cumulative hydration heat within 24 h and inhibit the drying shrinkage of CSA cement mortars. By contrast, calcined montmorillonite has a better shrinkage compensation than metakaolin, owing to that it contributes to the formation of ettringite. It is notable that low dosage of calcined montmorillonite can effectively decline the drying shrinkage of CSA cement mortar, whereas higher content is detrimental to the strength development. It lies in that calcined montmorillonite dramatically accelerates the initial heat evolution rate of CSA cement paste in 0.4 h and leads to a rapid setting. On the contrary, increasing amount of metakaolin prominently reduces the drying shrinkage of CSA cement mortar, with a slight shortening on the setting time.

Metabolic heat responses of Kluyveromyces marxianus and Saccharomyces cerevisiae during Carboxypeptidase Y Enzyme production

Kluyveromyces marxianus and Saccharomyces cerevisiae yeasts were compared for the production of Carboxypeptidase Y, a serine class glycoprotein exopeptidase (CPD-Y) using Bio calorimetry and Respirometric devices. The production medium components were optimized by Response Surface Methodology-based design of experiments. Bio calorimetric investigation combined with Respirometric studies suggested that the rate of heat evolution and respiration rate was directly linked to Dry Cell Weight (DCW), enzyme activity, and the consumption rate of the substrate. The Maximum yield obtained for K. marxianus and S. cerevisiae was 14 IU/mL and 8 IU/mL respectively which were threefold higher than the shake flask experiment. Yeast growth and nature of growth predicted using calorespirometric data fitted well with measured experimental results.

Fresh properties of 3D printed mortar with recycled powder

In this study, recycled powder (RP) was used to partly replace cement to produce the sustainable 3D printed mortar (3DPM). The properties of fresh 3DPM with RP of different replacement ratio (10%, 20% and 30%) were studied by conventional tests and 3D printer. At first, the flowability, setting time, mechanical property and hydration heat of fresh 3DPM with RP were investigated. Then 3DPM with RP was extruded and built by 3D printer to study the extrudability and buildability. The results show that the incorporation of RP in 3DPM leads to higher flowability losing rate with time, shorter open time, shorter initial and final setting time as well as rapid growth of penetration resistance stress with time. The maximum stress and the Young’s modulus of fresh 3DPM grow linearly with time at a lower replacement ratio, while there is a rapid growth when the replacement ratio is higher than 20%. Compared with 3DPM without RP, the maximum stress and Young’s modulus of 3DPM with 30% RP are increased 226.5% and 252.2% at 180 min, respectively. The addition of RP enhances the heat evolution rate and hydration heat in 8 h after mixing with water. The well correlation of hydration heat and fresh properties is obtained, which indicates that RP can be used in 3DPM to enhance the early age mechanical properties and buildability. 3DPM with 10%-30% RP has good extrudability and buildability.

Effect of direct carbonation routes of basic oxygen furnace slag (BOFS) on strength and hydration of blended cement paste

Mineral carbonation of alkali solid wastes is envisaged to be an effective method to sequester CO2 and turn the wastes into more valuable end products. Steel slag generated from the steel-making industry contains a high content of calcium oxide, which is a potential medium to sequestrate CO2 via the carbonation process. In this paper, the influence of reaction parameters including solid to liquid ratio, CO2 flow rate, temperature, volume of water and carbonation time on aqueous carbonation of basic oxygen furnace slag (BOFS) in maximizing CO2 sequestration was determined. The structural and mineralogical changes of carbonated BOFS were also analyzed using thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy. Using an optimized aqueous carbonation condition, about 16.35% of CO2 can be sequestered, which was obviously higher compared with dry carbonation (about 4.91%) at ambient conditions. Subsequently, the effect of replacing cement with carbonated BOFS (either by aqueous or dry route) on the micro-mechanical properties and hydration characteristics of blended cement paste was studied. The results demonstrated that as a small ratio of aqueous carbonated BOFS (10%-20%) blended in the cement paste they can accelerate the rate of early heat evolution during the first 24 h. On the contrary, as the carbonated BOFS ratio increased, the overall heat of hydration and mechanical strength were decreased. In comparison, BOFS carbonated by aqueous method is found to perform better in blended cement paste than its counterpart carbonated by dry method at the same replacement ratio due to the presence of a greater calcite content (acting as nucleation sites) in the aqueous carbonated BOFS.

An assessment of some physical properties of different brands of cement in Nigeria

The durability of infrastructures has become a significant issue starring the face of professionals in the building industry as most recently constructed structures are deficient in this regard. This study was carried out to assess the physical properties of five different brands of Portland cement commonly used in Nigeria. The specific surface method was adopted in obtaining the fineness, and the specific gravity bottle was used to determine the specific gravity of the different cement brands. The result shows that sample A had the highest fineness value of 360m2/kg and the only sample that met the ASTM standard value of 280 m2/kg. This implies that Sample A has a greater surface area for hydration which should lead to faster development of early strength and a higher rate of heat evolution. Sample E had the least fineness value of 168 m2/kg. This means that Sample E has the least surface area for hydration and should be slow in early strength gain. Sample B had the highest specific gravity value of 3.266 and the highest value of bulk density of 1462.085kg/m3. The implication is that Sample B has more moisture because it has the highest specific gravity value. The quantity of sample B that will be required in the concrete making will be less relative to other samples as it had the highest bulk density.

Effect of reactive MgO on hydration and properties of alkali-activated slag pastes with different activators

Activator type significantly affects the properties of alkali-activated slag (AAS) cement. Reactive MgO may have different effects on AAS cement activated with different activators. Four activators, sodium hydroxide (NaOH), water glass (WG), sodium carbonate (Na2CO3) and sodium sulfate (Na2SO4) were used in the present paper. The effect of reactive MgO on the fluidity, setting time of AAS paste and the compressive strength of AAS mortar was studied. The hydration process was assessed with pH and hydration heat. Microstructure and hydrates were also characterized by XRD, SEM and EDS. The results show that the addition of reactive MgO decreases the fluidity and setting time of AAS paste regardless of activator type. In NaOH activated slag, the compressive strength decreases with the increase of reactive MgO. While in the other three activators, there exists an optimal reactive MgO content of about 4%–6%. Now the compressive strength is higher. Reactive MgO increases the pH, heat evolution rate and cumulative hydration heat of AAS cement. Hydrotalcite and C-(A)-S-H gel are the main hydration products. More hydration products are promoted by reactive MgO, which results in the densification of AAS matrix. The above changes due to reactive MgO are especially remarkable for Na2CO3 and Na2SO4 activated AAS cement. AFt is more likely to be formed than hydrotalcite in Na2SO4 activated slag and reactive MgO enhances this trend. Reactive MgO is especially suitable for Na2CO3 and Na2SO4 activated AAS cement. It can accelerate the hydration, adjust the fluidity and setting time, and improve the mechanical properties to a reasonable degree.

Nano-TiO2 particles: a photocatalytic admixture to amp up the performance efficiency of cementitious composites

The utilization of nanoparticle-blended cement while producing concrete or mortar is gaining immense significance nowadays, mainly on account of the improvements in the long-term durability characteristics of the composites. The feasibility of using cement blended with nano- $$\hbox {TiO}_{2}$$ particles to produce less permeable or impermeable mortar and concrete of sufficient strength and durability requirements was investigated in the present study. The composite cement includes Ordinary Portland Cement replaced with $$\hbox {TiO}_{2}$$ nanoparticles at 0%, 2%, 4%, 6%, 8% and 10% quantities by weight. The properties studied include heat of hydration, compressive strength, bond strength, water absorption, permeability and sorptivity of mortar or concrete specimens. The roughness and surface defects of coarse aggregates greatly alleviated due to the incorporation of nano- $$\hbox {TiO}_{2}$$ particles in concrete specimens. The rate of heat evolution increased during early stages of hydration owing to the high fineness and additional reactive surfaces induced from the nano- $$\hbox {TiO}_{2}$$ particles blended in cementitious composite. Additionally, with reference to strength and durability characteristics, the nano- $$\hbox {TiO}_{2}$$ -blended composites performed relatively better than the control samples. The role of blended nano- $$\hbox {TiO}_{2}$$ cement composites in reducing the interconnected matrix porosity of concrete is discussed briefly, providing evidences from scanning electron microscope (SEM) observations.

Solution calorimetry to assess effects of water-cement ratio and low temperature on hydration heat of cement

This study investigated the effects of the water-cement ratio and low temperature on the hydration heat of cement using solution calorimetry. When curing at 20 °C, a lower water-cement ratio resulted in a higher cumulative hydration heat and hydration heat evolution rate at 24 h, but subsequently decreased. A lower water-cement ratio led to a lower cumulative hydration heat when curing at 5 °C and 0 °C. A higher water-cement ratio caused lower cumulative hydration heat when curing at −5 °C. The cumulative hydration heat of the cement paste increased with the curing temperature, and the influence of the negative temperature on the cumulative hydration heat of the cement paste increased with the water-cement ratio. The compound exponential model was used to predict the hydration heat of cement paste maintained above 0 °C. The results obtained by the logarithmic function model are in good agreement with the experimental results for curing at negative temperature.

Recycle option for metallurgical sludge waste as a partial replacement for natural sand in mortars containing CSA cement to save the environment and natural resources

The utilization of metallurgical sludge waste as a 10–30 % replacement of natural sand has been investigated in this paper for its effect on the initial setting time and hydration heat evolution of cement and the mechanical properties of mortars. The results revealed that the addition of metallurgical sludge waste increased the water demand by up to 30 %, delayed the initial setting time by 3 h for 10 %, to over 25 h for 30 % sand replacement, decreased the hydration heat evolution rate by 30 % for 30 % sand replacement, and negatively affected the mortars’ mechanical properties from 5 to 40 % for 20 % sand replacement, and from 30 to 50 % for 30 % sand replacement. For 10 % of sand replacement compressive strength was similar to the reference mortar. In order to obtain a shorter initial setting time, decrease the shrinkage and accelerate hydration heat evolution, part of the Portland cement (CEM I) was replaced by calcium sulphoaluminate cement (CSA). It was found that this method was effective for 20–30 % of CEM I replacement by 10 % of CSA and 10–30 % of CEM I replacement by 20–30 % of CSA in the case of setting acceleration, and for 10 % replacement in case of hydration heat evolution.

Influence of fly ash on mechanical properties and hydration of calcium sulfoaluminate-activated supersulfated cement.

This paper aimed to report the effects of fly ash (FA) on the mechanical properties and hydration of calcium sulfoaluminate-activated supersulfated cement (CSA-SSC). The CSA-SSC comprises of 80% granulated blast furnace slag (GBFS), 15% anhydrite, and 5% high-belite calcium sulfoaluminate cement (HB-CSA) clinker. The hydration products of CSA-SSC with or without FA were investigated by X-ray diffraction and thermogravimetric analysis. The experimental results indicated that the addition of FA by 10% to 30% resulted in a decrease in the rate of heat evolution and total heat evolution of CSA-SSC. As the content of FA was increased in the CSA-SSC system, the compressive and flexural strengths of the CSA-SSC with FA after 1 day of hydration were decreased. After 7 days of hydration, the compressive and flexural strength of CSA-SSC mixed with 10 wt.% and 20 wt.% of FA rapidly increased and exceeded that of ordinary Portland cement (OPC), especially the flexural strength. Moreover, the compressive strength of CSA-SSC mixed with 30 wt.% of FA after 90 days of hydration was close to that of OPC, and flexural strength of CSA-SSC mixed with 30 wt.% of FA after 7 days of hydration was close to that of OPC. The hydration products of the CSA-SSC and CSA-SSC mixed with FA were mainly ettringite and calcium silicate hydrate (C-S-H).

Characterization of Portland Cement Incorporated with FNS

The potential use of ferronickel slag (FNS) as supplementary cementitious material has been widely researched in recent years. Although much research was carried out on utilizing FNS as a binder, its advantages and disadvantages are still not clear. To properly use FNS as a cement replacement, this paper summarizes the following. (1) Changes expected on the oxide composition of FNS powder are due to the forming ores, fluxing stone, and cooling method. (2) The decreasing of the hydration heat evolution rate was detected by hydration heat evolution test and this is due to the low content of CaO and Al2O3 component in FNS. (3) It was found that the incorporation of FNS forms a dense pore structure more than cement mix and this is due to the secondary hydration reactions. (4) Hydration characteristics of FNS were assessed by pozzolanic reactions unexpectedly detected and incorporation of FNS creates C‐S‐H gel and hydrotalcite. (5) The development of strength was tested by compressive strength, splitting tensile strength, and flexural strength. From the results, the reduction of compressive strength was detected at an early age but substantially increasing at the long‐term curing ages. However, splitting tensile strength and flexural strength of concrete have shown various trends. (6) There is an improvement in the resistance to chloride penetration and sulfate attack while susceptible to carbonation. This is induced by the lowered pH in pore solution due to the reduction of Ca(OH)2 by substituting FNS binder. Finally, (8) ternary blended mixtures with conventional cementitious materials are an option to properly use FNS as a binder.

Study on the essential properties of recycled powders from construction and demolition waste

Recycled fine aggregates and waste powders can be ground into ultrafine powders, defined as recycled powders (RPs), for effective utilization of construction and demolition (C&D) waste. However, the performance of RPs relies on their original sources, the complex components of which hinder their applications. In this study, six common types of RPs were prepared from different sources of C&D waste with their properties comparatively examined in detail, including the chemical composition, micro morphology, fineness and hydration heat. Subsequently, the water requirements of standard consistence and setting time of pastes incorporating different RPs, together with the flowability and mechanical properties of the corresponding mortars were investigated. The results showed that the irregular and rough shapes of RPs required higher water consumption to achieve a standard consistency of paste. The higher alkali-content and lower content of SO3 of RPs contributed to the higher heat evolution rates of pastes with RPs in the first 30 min, but the pastes with RPs exhibited lower cumulative hydration heats than cement after 1d. The additional use of RPs decreased the flowability, density and strength of mortar. The mixed brick powder and clay brick powder had the relative positive impact on the mechanical properties of mortar at later ages, illustrating their great potential for use in cement matrix. The maximum reduction of strength was about 20% when the replacement ratio was limited to 30%.

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.

Heat of hydration of cement pastes containing high-volume fly ash and silica fume

This paper reports the effect of high-volume fly ash (low and high calcium types) with and without silica fume as Portland cement replacement on the heat of hydration of binary and ternary cement mixes. Both low and high calcium fly ash types were used to replace part of Portland cement at 50%, 60% and 70% by mass as binary cement mixes. The combination of fly ash and silica fume at 10% by mass as ternary cement mixes was also studied. The results indicated that low calcium fly ash retarded the rate of heat evolution more than high calcium fly ash at the same cement replacement levels. The total released heat reduction of about 70% can be achieved as Portland cement was replaced up to 70 mass% with low calcium fly ash. Total released heat of high calcium fly ash when compared to low calcium fly ash at 50%, 60% and 70% by mass of Portland cement replacement levels were higher by approximately 35%, 24% and 63%, respectively. The results confirmed that CaO content in fly ash had a significant effect on the hydration reaction of these cement mixes. In ternary cement mixes, in both low and high calcium fly ash, silica fume acted as a nucleation site that results to acceleration in the rate of heat evolution and total released heat more so than binary mix cement pastes, which contributed to the increase in early age compressive strength.

Functionalized polyester-based materials as UV curable adhesives

UV curable adhesives offer major advantages in comparison to other polymeric based adhesive systems, such as fast-curing rate and control of the polymerization heat evolution, being ideal for application on damaged tissues.Herein, functionalized polymers were prepared by modifying polycaprolactone diol (PCL) with an isocyanate-functional unsaturated acrylic ester, Laromer® 9000, using two different proportions. These functionalized materials were chemically/physically characterized and, after the addition of a biocompatible photoinitiator (Irgacure® 2959), were crosslinked by UV light irradiation. Such procedure allows the obtention of flexible transparent films. Films’ properties such as swelling, hydrolytic degradation, thermal stability, surface energy and adhesive capacity were evaluated. Furthermore, to assess the applicability of the films in biomedical applications, their haemocompatibility and biocompatibility were determined using human dermal fibroblasts as model.

Modeling early age hydration reaction and predicting compressive strength of cement paste mixed with expansive additives

Although expansive additives have been widely used to efficiently reduce shrinkage cracking in concrete, little research has been undertaken to model the hydration reaction of cement and expansive additive blends. This paper presents a hydration model that describes the hydration reaction that occurs when expansive additives are mixed at an early stage and an equation to predict the compressive strength of expansive concrete. Using the proposed model, this study predicted the hydration degree, rate of heat evolution, and gel/space ratio of the hardening cement–expansive additive paste. The results indicated good agreement of the calculated data with the measured data. From the relationship between the gel/space ratio and compressive strength, an equation was deduced for prediction of the development of compressive strength of expansive concrete. Furthermore, this work also found that the model parameters can be represented as a function of the mineral composition of the cement. The results demonstrate that the proposed model is effective and useful in predicting the hydration and mechanical properties of expansive concrete.