Low Hydration Heat Research Articles

Original behavior of pore water radiolysis in cement-based materials containing sulfide: Coupling between experiments and simulations

Blended cements with high content of blast furnace slag (CEM III/C) can be used for nuclear waste conditioning because of their low hydration heat as compared to ordinary Portland cements (CEM I). They however contain some sulfide, an impurity whose role needs to be investigated. Indeed, they can have an effect on the radiolytic H2 production under irradiation. To study the impact of sulfide species on H2 production, gamma irradiation, at a dose rate of 356 Gy h−1, was performed during 6 months in a closed system without O2 on a cement paste made with CEM III/C. At short time, the radiolytic H2 production rate is higher than that measured using CEM I. On the basis of reaction data collected in the literature on sulfur species, radiolysis simulations performed for both systems confirm this behavior. Moreover, they suggest that the sulfide concentration, initially imposed in pore solution by the slag is of the order of 180 mM, and is responsible for this H2 production. For the first two irradiation months, the following phenomena are then evidenced in CEM III/C: 1) conversion of sulfide into polysulfide anions; 2) pH increase; 3) production of H2 due to the H•+ H2S reaction having a very high rate constant. Nevertheless, in the medium term, the residual sulfide concentration is not sufficient any more for this mechanism to occur. It imposes a reducing environment, leading to a very efficient recombination of H2 in pore solution. The resulting equilibrium state is reinforced by the high liquid saturation level in the cement paste porosity. Therefore, even if the presence of sulfide species in blended cements momentarily increases the H2 production rate, it strongly reduces it at long times.

Controlling the heat evaluation of cement slurry system used in natural gas hydrate layer by micro-encapsulated phase change materials

Based on the low hydration heat requirement of cement slurry system used in natural gas hydrate layer and the shortcoming of traditional methods, a novel material, namely, micro-encapsulated phase change material (MPCM-1) was synthesized and used to regulate the temperature profiles and hydration heat of the cement slurry system by a physical method. During this study, the hydration heat was absorbed by MPCM-1 when the temperature of cement slurry system beyond the melting point of the phase change material (PCM), and then the hydration heat was released by the MPCM-1 when the temperature of cement slurry system drops below the crystallization point of PCM. The MPCM-1 containing low melting paraffin wax with urea formaldehyde resin shell was prepared by the method of in situ polymerization. At first, the structure of MPCM-1 was obtained by infrared spectrum analysis (FT-IR). Secondly, the phase change properties of MPCM-1 were measured by using a differential scanning calorimeter (DSC). As a result, it was shown that the melting point and heat of fusion of MPCM-1 is 23.09 °C and −97.49 J/g, respectively. Moreover, the thermal stability of MPCM-1 was obtained by using a synchronous thermal analyzer. Simultaneously, the surface morphology, particle size and distribution of MPCM-1 were also measured by using a scanning electronic microscope (SEM) and Laser particle size analyzer. Then, the MPCM-1 was introduced into the ordinary Portland cement slurry system to prepare a low hydration heat cement slurry system, the heat evaluation of cement slurry system were investigated by using a developed semi-adiabatic test equipment. The controlling effects of MPCM-1 on the heat evaluation of cement slurry system were investigated by the temperature profiles and hydration heat. Particularly, the temperature profiles were characterized by the initial temperature (Tin), temperature rise (Tr), maximum temperature (Tmax), and the hydration time (tmax) corresponding to the maximum temperature (Tmax), respectively. Besides, the effects of MPCM-1 on the mechanical strength of cement slurry system were also studied. As a result, it was shown that the use of the synthesized MPCM-1 reduced the Tr and Tmax of cement slurry system, it was also confirmed that the cement slurry system prepared by the synthesized MPCM-1 presented excellent mechanical properties.

Study on Effects of Different Replacement Rate on Bending Behavior of Big Recycled Aggregate Self Compacting Concrete

Big recycled aggregate self compacting concrete is a new type of recycled concrete, which has the advantages of low hydration heat and green environmental protection, but its bending behavior can be affected by different replacement rate. Therefor, in this paper, the research status of big Recycled aggregate self compacting concrete was systematically introduced, and the effect of different replacement rate of big recycled aggregate on failure mode, crack distribution and bending strength of the beam were studied through the bending behavior test of 4 big recycled aggregate self compacting concrete beams. The results show that: The crack distribution of the beam can be affected by the replacement rate; The failure modes of big recycled aggregate beams are the same as those of ordinary concrete; The plane section assumption is applicable to the big recycled aggregate self compacting concrete beam; The higher the replacement rate, the lower the bending strength of big recycled aggregate self compacting concrete beams.

Use of Algerian Natural Mineral Deposit as Supplementary Cementitious Materials

Much of the current research on concrete engineering has been focused on including siliceous additions as supplementary cementitious materials (SCMs). Silica reacts with Calcium hydroxide release during cement hydration, and produces more C-S-H. The latter contributes to increase compactness, mechanical strengths and sustainability of concrete. This paper explores the hydration characteristics of cement paste based on various natural mineral additions, that are very abundant in Algeria and present a high silica content (ground natural pozzolana “PZ” and ground dune sand “DS”). For this purpose, several analyses were carried out on modified cement pastes and mortars. TheseSCMswere introduced by replacement levels of 15, 20 and 25 by weight of cement. We first, studied the effect of these SCMs on the heat of hydration and mechanical strength of mortars at different ages. The evolution of hydration of modified paste was studied, by using Thermal analysis (TG/TDA) at different ages, to analyze the Calcium Hydroxide (CH) content of the modified pastes. It is shown that the CH content of the mixes including SCMs is lower than that of the plain cement paste, indicating that silica reacts with the cement paste through a pozzolanic reaction. Increased pozzolanic activity results in higher amounts of Calcium Silicate Hydrate in the paste, which in turn results in higher compressive strength for modified cement mortars. Due to its crystalline morphology, the ground DS particles present a partial pozzolanic effect, compared to PZ which is semi-crystalline. Modified mortars by 20% DS can be the optimal composition. It presents satisfactory results: good mechanical strength and low heat of hydration. It can lead to an economic and sustainable concrete. Ground DS is very abounded in Africa and free of any impurities and can be a good alternativeSCMsin cement industry.

La activación alcalina de diferentes aluminosilicatos como una alternativa al Cemento Portland: cementos activados alcalinamente o geopolímeros

Portland cement is considered an excellence building material. This is due mainly to its high performance, its good quality/price ratio and the raw materials from which it is made can be found almost everywhere in the world. However, the development of alternative Portland cements obtained through processes involves lower emission of CO2 into the atmosphere is a priority research and great interest worldwide. Alkaline activation constitutes an alternative to Portland cement, preferably amorphous or vitreous aluminosilicates and alkaline activator (such as NaOH, Na2CO3 or sodium silicates hydrates). The aluminosilicates may be natural products such as metakaolin or industrial by-products such as blast furnace slag or aluminosiliceous fly ash. These cements and concretes obtained by alkali activating aluminosilicates are characterised by high mechanical strength, low heat of hydration and high impermeability, as well as resistance to high and low temperatures and sulphate, seawater and acid attacks. Moreover, the preparation of these alkaline cements requires lower energy than in the manufacturing process of Portland cement. However, we still cannot say or establish that alkaline cements (alkali activated materials or geopolymers) are based on a clean chemical to the environment, due to production processes of alkaline solutions such as sodium silicates emit large amounts of CO2 into the atmosphere. This article aims to make a trip back in time to the origins of the alkali activation to explain the most characteristic and important chemical concepts.

Performances and working mechanism of a novel polycarboxylate superplasticizer synthesized through changing molecular topological structure

A novel star-shaped polycarboxylate superplasticizer (SPCE) was synthesized through a simple two-step method. 1H Nuclear Magnetic Resonance (1H NMR) and Infrared Spectroscopy (IR) measurements were used for structural characterization. SPCE and comb-shaped polycarboxylate superplasticizer (CPCE) with same molecular weights were designed and synthesized. The cement paste containing SPCE exhibited better fluidity, fluidity retention, water reduction, 25% lower saturated dosage of PCE, 10% longer setting time, lower hydration heat, more delayed hydration heat evolution and lower amount of hydration products at early ages. Furthermore, the adsorption behavior of SPCE and CPCE in cement pastes and the zeta potential were investigated, and then the working mechanism of SPCE was theoretically explained. It is interesting that changing topological structure from comb-shape to star-shape can achieve the optimization of dispersion effect, and further improve the working effectiveness. The aims of this study are to provide a new avenue to synthesize superplasticizer with novel structure achieving the chemical diversity of superplasticizer structure, and to verify the contribution of optimizing molecular shape. This new type of superplasticizer can be used as a rheology modifying agent in fresh cement-based materials.

Service Life Prediction of Bagasse ash Blended Concrete in Marine Splash Zone

Supplementary cementitious materials are commonly used in concrete due to their superior performance such as higher strength and low heat of hydration when compared to ordinary Portland concrete. In addition to pozzolanic benefits, utilization of these materials leads to durable and sustainable concrete. Although several pozzolanic materials are available including industrial by-products for use in concrete, their utilization is considerably restricted due to inadequate performance evaluation in concrete. Sugarcane bagasse ash is a by-product from the sugar industries that is directly disposed as a waste material which leads to significant environmental degradation. Pozzolanic characteristics of sugarcane bagasse ash have been evidently reported in the previous research studies. However, durability of bagasse ash blended concrete and its service life prediction are not reported in the existing literature. In the study, sugarcane bagasse ash was processed based on appropriate characterization scheme and bagasse ash blended cements were produced. Permeability of bagasse ash blended concrete was investigated and compared with Portland cement concrete and fly ash blended concrete. Moreover, influence of cover depth on service life of concrete structure was investigated. Results of accelerated durability test were correlated with the parameters influencing the long term performance of the concrete. The service life of bagasse ash concrete structures was found to be higher than the ordinary concrete structure in the same exposure conditions.

Monitoring of Kinetics of Pozzolanic Reaction

The pozzolanic additions are widely used as concrete component for numerous technical, economic and environmental reasons. Obviously the hydration process in a pozzolana containing system differs from hydration of Ordinary Portland Cement (OPC) what is indicated macroscopically by slower increase of strength and lower hydration heat. This paper aims to study pozzolanic reaction from perspective of chemical kinetics. From this point of view pozzolanic reaction and carbonation are two parallel reactions which are competing for portlandite (Ca (OH)2). The rate of each of these two reactions is characterized by rate constant and order of reaction. The system under study was 1:1 mixture lime – ceramic powder. The course of reaction was primarily studied by thermogravimetry which results were further subjected to kinetic analysis. MAS NMR spectroscopy was used for study of structural changes taking place in material in the course of pozzolanic reaction.

Abrasion erosion characteristics of concrete made with moderate heat Portland cement, fly ash and silica fume using sandblasting test

The abrasion erosion characteristics of concrete made from moderate heat Portland cement, fly ash, and silica fume were investigated via sandblasting test. In this study, the influences of fly ash, silica fume, impinging velocity and impinging angle on abrasion erosion resistance were taken into account. The test results indicated that the concrete fabricated with moderate heat Portland cement, fly ash and silica fume was applicable to the mass construction in need of either low hydration heat or high abrasion erosion resistance. The abrasion mass loss rate of concrete increased with the increasing of the impinging angle, and showed an exponential relation with the impinging velocity. Furthermore, the proposed method by Bitter and Neilson et al. was applied to analyze the abrasion erosion characteristics of concrete. The characteristics of each concrete mixture could be featured by four parameters (ε,φ,K, and n) according to this method, and they could be used for preliminarily predicting the abrasion erosion resistance of concrete.

Waste Diatomaceous Earth as Cementitious Binder Constituent

Paper is aimed at study of preparation possibilities of cementitious binders with waste diatomaceous earth. In the first step, the influence of ground diatomaceous earth on properties of cement mixture was studied. In the next step, diatomaceous earth was calcinated and, lastly, the influence of replacing FGD-gypsum with anhydrite II as a setting controller in the mixture containing calcined diatomaceous earth was monitored. Technological properties of the prepared mixtures were measured and compared with cement standard. For studying the influence of phase composition and microstructure of cements hardened by both untreated and calcinated diatomaceous earth, hardened cements were tested by DTA and their porosities were measured. The results show that it is possible to prepare binder containing calcinated diatomaceous earth which has slightly lower early strengths but higher long-term strengths and lower hydration heat development.

Temperature variation in concrete samples due to cement hydration

Large structures of massive concrete are an engineering problem due to cracking created by thermal stresses. Nowadays, many constructions use large amount of concrete, like dams, tall buildings and infrastructure solutions. In big concrete structures, the temperature gradient is mainly caused by cement hydration heat. Concrete properties also directly affect the temperature gradient. To prevent cracking in concrete structures, some technical approaches can be done, such as choosing cooler raw materials or precooling (ice) or pipe cooling, or applying superficial thermal insulation. Cracks will reduce the safety, integrity and durability of the structure. Besides, repairing a crack is very difficult. This paper focus on identifying which properties influence the concrete temperature and on how raw materials affect the thermal characteristics. Experimental tests have been done to analyze how the precooling technique and cement type reduce the temperature’s gradient. The numerical simulation contributed to the understanding of the temperature behavior in several points in the specimen. There was a reasonable agreement between the experimental results and those obtained by numerical simulation. The use of cement with low hydration heat, the concrete in lower height layers and the use of ice were the main properties evaluated, and they all caused a reduction in temperature. However, the biggest difference was noticed in lower height layers of concrete. The use of concrete in several layers was the best option for decreasing temperature.

Study on the performance and mechanism of accelerators LSA-1 and LSA-2 for deepwater well cementing at low temperatures

There are abundant hydrocarbon resources in the deepwater region, so the exploration and development of deepwater oil and gas has become an important strategy for the Chinese petroleum industry. However, well cementing in deepwater, especially the cementing of the surface casing, is challenged due to the low temperature, which requires proper cementing accelerators to make the cement have certain strength at the early stage. Aiming to enhance the cementing quality of the surface casing, two kinds of lithium salt accelerators named LSA-1 and LSA-2 were developed in our early works based on the effects of different salts on oil well cement at low temperatures. In this paper, a comprehensive set of experiments was designed to test the effects of LSA-1 and LAS-2 on the Class-G oil well cement, including observations and measurements of the cement hydration products, the hydration heat and the developments of the static gel strength and the compressive strength. Based on these experiments, we discussed the mechanisms and performances of these two lithium salt accelerators at low temperatures. The experiment results indicate that both LSA-1 and LSA-2 can accelerate the hydration rate by advancing the hydration acceleration period and result in the earlier generation of Ca(OH)2 and AFt. They can also induce the cement hydration products to form regular and compact gel structures, which contributes to the development of the static gel strength and the compressive strength of cement slurry at the early stage. Moreover, the two lithium salt accelerators have the characteristic of low hydration heat. This is helpful to reconcile the contradiction between the development of cement early compressive strength and the hydration heat, which can help to avoid channeling and hydrate decomposition in the strata containing gas hydrate. In general, LSA-2 has a stronger effect on accelerating hydration of oil well cement, while LSA-1 has less impact on cement hydration heat. Therefore, both LSA-1 and LSA-2 are qualified to serve as low-temperature accelerators for deepwater cementing, which are able to meet the diverse requirements of the deepwater low-temperature environment and the field cementing operation.

β-Belite cements (β-dicalcium silicate) obtained from calcined lime sludge and silica fume

The utilization of lime sludge (LS), a pulp and paper industry residue, and silica fume (SF), a ferrosilicon industry by-product, as raw materials for the preparation of β-dicalcium silicate (β-C2S or β-belite) is investigated. β-phase belite is synthesized in a molar ratio of calcined LS/SF at 2.0 by hydrothermal method followed by calcination at 1000 °C for 2 h, which is lower temperature than conventional production temperature of about 1200 °C, and importantly without any chemical stabilizers. The produced belite cements containing 89.3% of β-belite, the rest being α-belite (5.93%), tobermorite (C–S–H, 1.71%), cristobolite (SiO2, 1.83%) and free lime (CaO, 1.24%). The micro analytical characteristic of the raw materials and formed belite are examined by means of TG-DTA-DTG, XRF, XRD, SEM with EDAX, FT-IR, BET techniques and isothermal conduction calorimetry. The hydration of pastes and compressive strength of mortars of the formed β-belite blended with ordinary Portland cement are studied with a partial replacement of cement by 10%, 20% and 30%. The reaction of β-belite in combination with Portland cement is comparable up to 10% replacement of cement to the pozzolanic reactions of other materials used in similar ways. However, it is observed that the premature stiffening of belite incorporated cement pastes takes place with low heat of hydration because of higher reactivity of belite cement incorporation.

Comparison of the properties between high-volume fly ash concrete and high-volume steel slag concrete under temperature matching curing condition

Massive concrete structures tend to have high cracking risk due to early temperature rise. High-volume mineral admixture concrete, which has low hydration heat, is suitable for massive concrete structures. In this paper, the properties of high-volume fly ash (HVFA) concrete and high-volume steel slag (HVSS) concrete were compared under two different curing conditions (standard curing condition and temperature match curing condition). The results show that the promoting effect of temperature match curing on the early strength of HVFA concrete is more obvious than that on HVSS concrete. Temperature match curing has negative effect on the late strength and elastic modulus of HVSS concrete. The promotion of temperature match curing to the elastic modulus development is not so obvious as that to the strength development. Temperature match curing can significantly decrease the chloride permeability of HVFA concrete, but its influence on the chloride permeability of HVSS concrete is inconspicuous. Though the adiabatic temperature rise of HVSS concrete is lower than that of HVFA concrete, which is beneficial to its application to the massive concrete structures, its strength especially the splitting tensile strength and resistance to chloride ion penetration need to be improved.

Estudo sobre redução do consumo de cimento e emissão de co2 para concreto de alto desempenho

This work presents an analysis for preparation of high performance concretes with low consumption of Portland cement, and evaluates some of its properties in fresh: spreading, resistance to segregation and ability to pass; and hardened (mechanical properties): compressive strength, diametral tensile strength in compression and elastic modulus. The production of concretes with low consumption of cement Portland enables an increased sustainability in the Civil Industry based on concrete, with increased longevity of raw materials deposits, reduction of CO2 emissions and no consumption of energy and lower transportation cost. It provides several technical improvements, as lower heat of hydration, shrinkage and cracking. Based on packaging concepts and particulate dispersion, suitable choice of materials and use of mineral fillers and additions there were obtained concretes with low consumption of cement and high resistance, with relative consumption of binder materials less than 5 kg/m³ to produce 1 MPa of compressive strength. It was used the dosage methodology presented by Gomes (2002) and it was concluded that it is possible to produce a high performance concrete with reduced Portland cement consumption. Keywords: High performance concrete, Low cement consumption, Strength, Precast elements.

Performance evaluation of sugarcane bagasse ash blended cement in concrete

By-products from a number of industrial processes are used as alternative supplementary cementitious materials in concrete. Sugarcane bagasse ash is mainly composed of amorphous silica and can be used as a pozzolanic material in concrete. Production of sugarcane bagasse ash (SCBA) based blended cements with different replacement levels of SCBA, and the performance of concrete with these cements in terms of compressive strength, heat of hydration, drying shrinkage and durability are discussed in this paper. Durability performance was investigated by five different methods in this study, namely oxygen permeability test, rapid chloride penetration test, chloride conductivity test, water sorptivity test, DIN water permeability test and Torrent air permeability test. The results from this study show that use of sugarcane bagasse ash in concrete prominently enhances its performance. Low heat of hydration, additional strength gain due to pozzolanic reaction, significant reduction in permeability because of pore refinement and similar drying shrinkage behavior were observed for bagasse ash blended concrete compared to control concrete.

Heat of hydration of concrete containing powdered scoria rock as a natural pozzolanic material

Specifications for mass concrete constructions typically mandate the use of pozzolanic materials with a low heat of hydration. In this paper, the influence of different powdered scoria rocks on reducing the heat of hydration and the associated temperature rise in mass concrete was investigated. Six paste mixtures, including a control and mixtures containing three sources of powdered scoria rocks (SR1, SR2, SR3), fly ash (FA) and ground silica flour (GS), were investigated using isothermal calorimetry. Also, the temperature rise due to the heat of hydration of their corresponding concrete mixtures cast in a semi-adiabatic block was recorded. The compressive strength development and microstructure of concrete mixtures were examined. The results show that powdered scoria rocks were as effective as FA in reducing the heat of hydration and peak temperature rise and can be used as a source of natural pozzolan for mass concrete applications.

Development of fly ash-based composite binder and its application in construction materials

The effect of addition of metakaolin on hydration and physico-chemical properties of fly ash composite binder prepared by blending 50–60% fly ash with hydrated lime sludge, Portland cement and gypsum plaster were investigated. The metakaolin has a beneficial effect on the properties of composite binder by reducing its porosity and pore diameter with curing period which are responsible for the attainment of high strength and better stability towards water over the composite binder without metakaolin. The strength development in composite binder takes place due to the hydration of gypsum plaster to gypsum and pozzolanic reaction of fly ash, metakaolin with lime and alkali in cement thereby forming ettringite, tobermorite and C4AH13. The reaction products formed during the hydration were confirmed by X-ray diffraction, differential thermal analysis and scanning electron microscopy. The composite binder has low heat of hydration and is found suitable for use in masonry works, concrete and bricks.

Rock-filled concrete, the new norm of SCC in hydraulic engineering in China

Rock-filled concrete (RFC) was developed in China in 2003 as an application of self-compacting concrete (SCC) that can then be used as “normal” concrete for massive concrete constructions. RFC is produced by filling the voids of rock blocks with SCC, which has good fluidity and segregation resistance. To guarantee the required workability of SCC, a mix design method for SCC based on its paste rheological characteristics was developed. The proposed method yielded practical benefits by saving on the amount of laboratory work, testing time, and raw materials. The integrated performance of RFC was studied by conducting tests on its compaction, compression strength, tensile strength, and permeability. Results indicated that RFC meets the requirements of hydraulic concrete. With two types of construction technology in practical application, RFC exhibits remarkable advantages, such as high construction efficiency, low cost, low heat of hydration, and low environmental load. These advantages contribute to a simpler construction management and an easier quality control, signifying that RFC is a promising technology in hydraulic engineering.

Study of Increasing of Belite Reactivity

Within the research at Institute of Technology of Building Materials and Components the questions of belite cement hydration speed improvement have been solved for a long time. In comparison with common Portland cements (alite type) these cements obtain almost identical final properties but the main shortage of them due to which they are not practically produced is their very low hydration process speed and thus insufficient initial strength for construction practice. A development of lower hydration heat is another difference of the belite cement from common Portland cements. In case of concreting of massive constructions as for example water dams this can be perceived as an important benefit, however in case of concreting during cold season of the year this appears as a definite negative. The belite cement also shows a lower inclination to concrete efflorescence and higher strength to aggressive environment due to lower CaO content. Both of the properties can be definitely understood as benefits compared to orthodox alite clinker. The raw material base of belite cements require less lime than production of common Portland cements and on that ground the implementation of its production would be a positive benefit for ecology in sense of CO2 emission reduction and also in improvement of economy of non-renewable raw material sources. The raw material is burnt to lower temperature than alite cement resulting in lower CO2 emission released in the atmosphere during the cement production. In addition at reduction of the temperature for more than 100 °C also heat consumption is reduced for 10 to 14 %, which has positive economical and ecological effects due to lower consumption of fuels. Within the research focussed on improvement of belite cement properties the study of hydration process course and technological properties of belite (C2S) prepared using low-energy burning modes was the aim of the research.