Portland Cement Hydration Products Research Articles

Phase Composition of Hydration Products of Portland Cement Mechanically Activated in a Vortex Layer Apparatus with Additives of Various Nature

Phase Composition of Hydration Products of Portland Cement Mechanically Activated in a Vortex Layer Apparatus with Additives of Various Nature

Revealing the difference between creep behavior of hydration products of Portland cement and alkali-activated slag paste at early age

This study investigates the early-age creep behavior of various gels in Portland cement (PC) and alkali-activated slag (AAS) pastes. The objective is to reveal the correlation between the composition and creep behavior of hydration products in these two systems. The results indicate that the creep modulus of C-A-S-H in AAS is significantly lower than that of outer products (Op) and inner products (Ip) in PC paste, even though Op exhibits higher elastic modulus than C-A-S-H. The intermixed CH has a more pronounced effect on the creep modulus of Op compared to its elastic modulus, which should be mainly attributed to the pinning effect of CH during the deformation of Op during the creep process. The lack of enhancement by high stiffness crystal phases in the matrix of AAS leads to the relatively low creep modulus of C-A-S-H.

Synergic effect of recycled aggregate, fly ash, and hydrated lime in concrete production

The use of construction and demolition waste (CDW) as recycled aggregate (RA) and fly ash (FA) in the composition of cementitious materials can make the resulting concrete more sustainable. However, RA is more heterogeneous, porous, and less dense than the natural aggregate (NA), influencing the mechanical strength. On the other hand, the reaction of FA with hydration products of Portland cement is slow, delaying the strength development at an early age. An alternative to increase the strength of concrete with FA at an early age is using the hydrated lime (HL). This research intends to evaluate the efficiency of adding HL in concrete with RA and FA. In this way, this research intends to evaluate the efficiency of adding HL in concretes with RA and FA and comprises two stages. First, a w/c ratio of 0.55 and a replacement of 50% natural coarse aggregate by concrete recycled aggregate (CRA) and mixed concrete aggregate (MRA) was established, considering similar compressive strengths. In the second stage, the properties of concretes with 20% FA in partial replacement of Portland Cement (PC), adding HL at 5% and 10% (by mass) were evaluated. The results showed that concretes with CRA present performance better than concretes with MRA, and the effect of HL was significant for all properties investigated. Concretes with CRA, FA, and 10% HL improved the compressive strength by 12.47%, reduced water absorption and porosity by 9.87% and 23.82%, respectively, and increased apparent density by 8.77% compared to the mixture without HL. The SEM analysis showed the beneficial effect of HL in concretes with RA, due to the high availability of calcium hydroxide. For concretes with RCA, a reduction in the mean equivalent diameter of 62.29% was verified; for concretes with MRA, this reduction was 23.25%. A reduction of carbonation depth was observed when concretes with MRA, FA and 10% HL showed a carbonation coefficient 44.5% lower than concrete without HL after 35 days of exposure to CO2, while concretes with CRA presented a carbonation coefficient of 87.7% lower.

Investigation on strengths and hydration products of portland cement blending with dolomite powder and metakaolin at 20 °C and 60 °C

This study aimed to understand the synergistic effect of dolomite powder (DM) and metakaolin (MK) on the strengths and hydration products of Portland cement (PC), then facilitating DM application in PC. Results showed that the combination of DM and MK improved the flexural and compressive strengths of mortars at 20 °C and 60 °C markedly. This was mainly due to that the combined effect of DM and MK improved the pore structure. At 20 °C, the incorporation of MK in the PC-DM pastes stimulated the generation of calcium carboaluminate including hemicarbonate (Hc) and monocarbonate (Mc). An increase in the MK to DM ratio resulted in the increment of Hc at the early age. At the later age, further dissolution of DM promoted the transformation of Hc to Mc. At 60 °C, hydrotalcite (Ht) was found in the pastes with low MK dosages (≤5 wt%), and Ht was mainly distributed in the DM particle surface. However, the additions of high MK dosages (≥10 wt%) restricted the formation of Ht. The lack of portlandite might be the major reason for the limitation of Ht formation. In addition, iron containing calcium carboaluminate could be identified in the PC-DM-MK system cured at 60 °C, especially with high MK dosages.

Thermodynamic, mechanical, and electronic properties of ettringite and AFm phases from first-principles calculations

The aluminate containing hydration products of Portland cement, mainly referring to ettringite and AFm phases (AFm, Mc, Hc and Friedel’s salt), are important for chloride chemical binding and microstructure development of cement pastes since they are easily transformed with different additives and solutions. First principles calculations are employed to find their thermodynamic equilibrium crystal structures. Various equivalent hydrostatic pressures are applied onto these structures to study their volume change, thermodynamic and elastic moduli. Among them, Mc shows the smallest interlayer space, highest volume stability, density, elastic modulus, and stiffness property. The volume of hydrated phase can increase by 12.5 % due to the conversion from Mc to Friedel’s salt. Electronic properties suggest that there are non-bonding electrons in the O-p orbitals of CO32– in the Mc and charge transfer from CO32– to the Ca2+ made the bonding states between O-p of CO32– and Ca-d stronger. This could provide a theoretical basis for improving the mechanical and durability properties of concrete by adding supplementary cementitious materials, such as limestone powders appropriately.

Insights at the neutron irradiation-induced structural homogenization effect of calcium silicate hydrates and degradation mechanism of mechanical properties: a molecular dynamics study

Concrete has been widely applied in nuclear facilities, however, knowledge about the degradation mechanisms of cementitious materials due to irradiation is still limited. Therefore, in this work, molecular dynamics was employed to investigate the influence of irradiation energy on the structure and mechanical performance of calcium silicate hydrates (C-S-H, primary hydration products of Portland cement). Simulation results indicate irradiation leads to an isotropic structure transformation of C-S-H. The strength and stiffness of C-S-H along the in-plane direction was substantially reduced by irradiation, regardless of compression or tension loading. It is caused by the shortening of mean chain length of silicate tetrahedra, as well as the increase in the number of cracks and pores. Furthermore, an increase in the ductility of C-S-H is also observed, which is related to reorganizations and re-polymerizations of silicate tetrahedra on high-stress conditions. The mechanisms interpreted here pave the way to designing more irradiation-resistant cement-based materials.

ИССЛЕДОВАНИЕ ХИМИЧЕСКОГО ВЗАИМОДЕЙСТВИЯ СТЕКЛОВОЛОКНА С ПРОДУКТАМИ ГИДРАТАЦИИ ЦЕМЕНТА

Reinforcement of concrete with fiberglass improves the performance properties of concrete. The object of the study is fiberglass concrete, where Portland cement or alumina cement is used as a binder, and silica fiberglass is used as a filler. The chemical and phase compositions of Portland cement and alumina cement have been studied. The influence of the products of hydration of Portland cement and alumina cement on the chemical resistance of glass fiber has been investigated. The phase composition of Portland cement and alumina cement after hydration is studied using X-ray phase analysis. It is revealed that the following phases are present in alumina cement: CaОAl2O3, MgОAl2O3, 12CaO•7Al2O3, 2CaO•Al2O3•SiO, the phase composition of Portland cement is Ca6Al2(SO4)3(OH)12•12H2O, Ca2,25(Si3O7,5(OH)1,5)•(H2O), Ca(OH)2, CaCO3. It has been found that when hydrated, Portland cement has a negative effect on fiberglass due to the presence of Ca(OH)2 in it. The phase composition of the alumina cement after hydration shows the absence of Ca(OH)2. The chemical composition of fiberglass is investigated using X-ray fluorescence analysis. The use of alumina cement when using non-alkali-resistant fiberglass in a composite material is substantiated. The study of the stability of fiberglass in the environment of cement drawing has been carried out. Studies have shown that KV-11 grade fiberglass interacted less with hydration products of alumina cement than with hydration products of Portland cement.

Influence of Glass Powder Additives on the Hydration Process of Portland Cement

This article presents the results of microcalorimetric studies of the process of the interaction of the hydration products of Portland cement with additives of glass powders of various chemical compositions. It is found that when glass is added in a powder state, an increase in the rate of hydration of Portland cement is observed.

Structure and Mineral Composition of Soil Cement Based on Kaolinite Clay Modified with a Complex Hydrophobic–Plasticizer Additive Based on Polycarboxylate Ether and Octyltriethoxysilane

The effect of polycarboxylate ether and a complex hydrophobic–plasticizer additive on the structure and mineral composition of soil cement based on kaolinite clay with kaolinite content of more than 95% was studied. Research methods included X-ray phase analysis, differential scanning calorimetry, and electron-scanning microscopy. Patterns of the effect of polycarboxylate ether and a complex hydrophobic–plasticizer additive on the formation of Portland cement hydration products in strengthened clay were determined, and changes in the structure of modified samples of soil cement based on kaolinite clay were revealed.

Nanostructure and Fracture Behavior of Carbon Nanofiber-Reinforced Cement Using Nanoscale Depth-Sensing Methods.

In recent years, carbon nanofibers have been investigated as a suitable reinforcement for cementitious composites to yield novel multifunctional materials with improved mechanical, electrical, magnetic, and self-sensing behavior. Despite several studies, the interactions between carbon nanofibers and Portland cement hydration products are not fully understood, with significant implications for the mechanical response and the durability at the macroscopic lengthscale. Thus, the research objective is to investigate the influence of carbon nanofibers on the nanostructure and on the distribution of hydration products within Portland cement paste. Portland cement w/c = 0.44 specimens reinforced with 0.0 wt%, 0.1 wt%, and 0.5 wt% CNF by mass fraction of cement are cast using a novel synthesis procedure. A uniform dispersion of carbon nanofibers (CNF) via a multi-step approach: after pre-dispersing carbon nanofibers using ultrasonic energy, the carbon nanofibers are further dispersed using un-hydrated cement particles in high shear mixing and mechanical stirring steps. High-resolution scanning electron microscopy analysis shows that carbon nanofibers fill nanopores and connect calcium–silicate hydrates (C–S–H) grains. Grid nano-indentation testing shows that Carbon nanofibers influence the probability distribution function of the local packing density by inducing a shift towards higher values, = 0.76–0.93. Statistical deconvolution analysis shows that carbon nanofibers result in an increase in the fraction of high-density C–S–H by 6.7% from plain cement to cement + 0.1 wt% CNF and by 10.7% from plain cement to cement + 0.5 wt% CNF. Moreover, CNF lead to an increase in the C–S–H gel porosity and a decrease in both the capillary porosity and the total porosity. Based on scratch testing, adding 0.1 wt% CNF yields a 4.5% increase in fracture toughness and adding 0.5 wt% CNF yields a 7.6% increase in fracture toughness. Finally, micromechanical modelling predicts an increase of respectively 5.97% and 21.78% in the average Young’s modulus following CNF modification at 0.1 wt% CNF and 0.5 wt% CNF levels.

Modelling of sand cement hydration in normal conditions

The paper considers the hardening mechanisms of the sand cement composition (0.75 sand and 0.25 Portland cement) during 28 days. In this study, the VCCTL tool is used for computer modelling of the sand cement hardening process. It is found that after 28 days, the sand cement hydration is ∼0.75, the porosity is over 0.20 and 0.32 at the water-cement ratio of 0.40 and higher, respectively. Calcium silicate hydrate (C–S–H) and portlandite (CH) are the main hydration products of Portland cement and responsible for the sand cement strength. Owing to the high porosity of sand cement, free moisture is present in it in large quantities. It is shown that the effective elastic moduli of sand cement rapidly grow during 200 hours and then monotonically lower. The yield stress monotonically grows during sand cement curing, and at 0.40 and 0.44 water-cement ratios achieves the maximum value. This growth thus depends on the water-cement ratio and affects Young’s modulus during the curing process. At the qualitative level, a correlation is observed between the yield stress and Young’s modulus depending on the curing time of sand cement with the discussed water-cement ratios.

The effect of microencapsulated phase change materials on the rheology of geopolymer and Portland cement mortars

AbstractThe effect of microencapsulated phase‐change materials (MPCM) on the rheological properties of pre‐set geopolymer and Portland cement mortars was examined. Microcapsules with hydrophilic and hydrophobic shells were compared. The shear rate dependency of the viscosities fitted well to a double Carreau model. The zero shear viscosities are higher for geopolymer mortar, illustrating poorer workability. The time evolution of the viscosities was explored at shear rates of 1 and 10 s−1. New empirical equations were developed to quantify the time‐dependent viscosity changes. The highest shear rate disrupted the buildup of the mortar structures much more than the lower shear rate. Microcapsules with a hydrophobic shell affect the rheological properties much less than the microcapsules with a hydrophilic shell, due to the higher water adsorption onto the hydrophilic microcapsules. Shear forces was found to break down the initial structures within geopolymer mortars more easily than for Portland cement mortars, while the geopolymer reaction products are able to withstand shear forces better than Portland cement hydration products. Initially, the viscosity of geopolymer mortars increases relatively slowly during due to formation of geopolymer precursors; at longer times, there is a steeper viscosity rise caused by the development of a 3D‐geopolymer network. Disruption of agglomerates causes the viscosities of portland cement mortars to decrease during the first few minutes, after which the hydration process (increasing viscosities) competes with shear‐induced disruption of the structures (decreasing viscosities), resulting in a complex viscosity behavior.

Features Of The Formation Of The Structure And Properties Of Aerated Concrete Due To Its Forced Carbonate Hardening

The results of experimental studies on the establishment of the possibility of using carbon dioxide in the production of concrete for the purpose of improving its strength characteristics are presented. Specific features of physicochemical transformations occurring in the body of porous concrete during the organization of its hardening in environments with a high concentration of carbon dioxide are revealed. It was found that when lime is introduced into the cement binder composition, the degree of carbonation of portland cement hydration products decreases. It was shown that with successive steaming and forced carbonization of porous concrete on the basis of cement and cement-lime binder, conditions for both hydration and carbonate hardening are provided. This causes the appearance of a maximum amount of crystalline hydrate and carbonate neoplasms, which increases the strength of the material. The revealed features of the physicochemical processes of carbonization of cement and cement-lime systems allow us speak about the effectiveness of the use of man-made CO2 in the technology of production of unreinforced concrete products.

Environmental and Economical Aspects of Partial Replacement of Ordinary Portland Cement with Saudi Raw Minerals

This study aims to utilize a local natural mineral material from different places in western area of Saudi Arabia namely, (Osfan, Alkamel, Wadi starah, Khulais, Jeddah and Alghowla) as a partial replacement of Ordinary Portland Cement (OPC) in order to increase its productivity, minimizing the problems associated with its production in terms of energy consumption and air pollution. In addition to the reference sample (C:100% wt. OPC), other six mixes were prepared containing 75 wt.% of OPC and 25 wt.% of each raw mineral. They were denoted as C1, C2, C3, C4, C5 and C6. Different cementing, sintering, chemical and mechanical properties of the prepared mixes were tested according to the international standard specifications. It was concluded that OPC blended with 25 wt.% of local natural minerals from Jeddah (C5), Wadi starah (C3) and Alkamel C2 show outstanding cementing and mechanical properties compared with the reference sample. They recorded relatively longer setting time ranges 55–160, 52–145 and 52–144 min respectively compared with the reference sample (C) which recorded only 48–120 min. Relatively higher percent of combined water (23.75–28.23, 20.84–24.59, 16.34–19.31%), respectively at different ages of hydration, compared to the reference sample (C) that recorded 15.59–18,00%. The samples showed higher heat of hydration 81–97, 77–94, 75–90 cal/g, compared with reference sample which recorded 70- 85 cal/g, higher bulk density 1.61–1.96, 1.66–1.84 and 1.65–1.84 g/cm3, respectively compared with the reference sample that recorded 1.61–1.84 g/cm3, lower apparent porosity of (10.41–15.02, 12.75–16.25, 13.96–17.40%), respectively whereas the reference sample noted (14.39–24.11%) and relatively higher values of compressive strength (90–125, 80–120, 75–113 kg/cm2), respectively compared with the reference sample which recorded (60–110 kg/cm2). The remaining samples C1, C4 and C6 showed less cementing and mechanical properties compared with the reference sample (C). The improved properties of C5, C3 and C2 are due to their relatively higher content of portlandite mineral {Ca(OH2)} one of the main hydration products of Portland cement, as well as their relatively better microstructure.

The material characterization and gamma attenuation properties of Portland cement-Fe3O4 composites for potential dry cask applications

The effect of nanosized magnetite (Fe3O4) additions on the microstructural, mechanical and gamma attenuation properties of White Ordinary Portland cement (WOPC) pastes was investigated. The microstructure of a set of cement composites with Fe3O4 content ranging from 0 to 50 wt% was examined using X-ray diffraction and Scanning Electron Microscopy (SEM) techniques. Magnetite additions did not influence the hydration products of Portland cement after 28 days of curing. SEM showed uniform distribution of magnetite nanoparticles in the cement hydration products of composites with less than 10 wt% Fe3O4. Aggregation of magnetite nanoparticles occurred when high loading of magnetite was added to the cement (20, 40 and 50 wt%). Compressive strength and stress-strain curves were also measured to characterize the mechanical performance of the composites. A maximum compressive strength of 60 MPa was obtained for cement pastes reinforced with 10 wt% Fe3O4, which represents an enhancement of 50% over the plain WPOC paste. Composites loaded with 50 wt% Fe3O4 yielded to a reduction of compressive strength (35 MPa) of 5% over the reference paste. Mechanical behavior of the material was explained in terms of their microstructure, i.e. uniform magnetite embedded in the paste has a reinforcement effect due to the promotion of hydration process and the filling effect of the particles. Heterogeneous distribution of magnetite particles due to agglomeration acted to weaken the cementitious matrix by creation of pores. Finally, transmission experiments and Monte Carlo simulations were conducted to evaluate the shielding properties of the composites when exposed to a Cs-137 gamma source (0.662 MeV). The addition of Fe3O4 improves the shielding capability of Portland cement pastes with enhancements ranging between 3.1 and 2.6% for samples with 2.5 and 50 wt% Fe3O4 respectively. No simple relationship exists between the attenuation properties and magnetite loading. Changes in the attenuation coefficients of the composites are explained in terms of the chemical composition and microstructural effects.

Performance of copper slag contained mortars after exposure to elevated temperatures

Performance of copper slag contained mortars after exposure to elevated temperatures is studied in this paper. Portland cement (PC) based mortar with copper slag replacements of 0, 5%, 10% and 15%, as well as NaOH activated copper slag mortar with NaOH concentrations of 6 M, 8 M, 10 M and 12 M were manufactured. Compressive strength and flexural strength of the mortar specimens were tested at room temperature and after exposure to 200 °C, 400 °C, 600 °C, 800 °C, 1000 °C and 1200 °C, respectively. Paste specimens were further prepared to measure their chemical and physical changes with temperature by using X-ray diffraction (XRD), thermal gravity (TG)/differential scanning calorimeter (DSC) and scanning electron microscopy (SEM)/SEM-energy dispersive spectrometer (EDS) techniques. The results show that the strength of PC mortars containing copper slag increased within 200 °C, but after that their strength declined continuously. While the strength of alkali activated copper slag mortars increased dramatically both within 200 °C and after 800 °C. Amorphous Fe(OH)3/Fe(OH)2 gels could be formed in the hydration products of PC containing copper slag at room temperature and of alkali activated copper slag at a higher temperature. For alkali activated copper slag, after 600 °C, Fe2O3 was formed as a result of the oxidation of Fe2SiO4 and/or the decomposition of Fe(OH)3/Fe(OH)2. With the further increase of temperature, Fe2O3 could have melted in a Na-rich environment. The melted matters could sufficiently flow through the pores and cracks in the matrix. When the matters cooled down, they could fill in the pores and cracks and then make the matrix much dense to provide high strength.

Interaction of Portland cement hydration products with complex chemical additives containing fiberglass in moisture-proof cement compositions

Interaction of Portland cement hydration products with complex chemical additives containing fiberglass in moisture-proof cement compositions

The Improvement of the Pozzolanic Properties of Recycled Glass during the Production of Blended Portland Cements

The replacement of primary raw materials in cement production is a relevant topic today. One potentially usable raw material is recycled glass. The disadvantage of glass is its tendency towards aggregation. Due to this phenomenon fine glass incement composites work only physically and mechanically as filler rather than as an active pozzolan. The possibilities of improving the pozzolanic properties of recycled glass by means of new milling techniques were examined in this paper. Next to the pozzolanic activity of recycled glass, the advancement of the hydration process of the binder and the effect on the physical and mechanical properties were also monitored. A combination of a ball mill and a nontraditional high-speed pin mill DESI 11 was selected for sample preparation. Portland clinker and recycled glass mixed at a ratio of 80: 20wt. % were used for the preparation of the blended cement. The pozzolanic activity of the pure recycled glass was evaluated using a modified Chapelle test. The hydration process of glass grains in the cement composite was observed using an SEM with an EDX probe. The effect of the grinding technology on the cement rheology and on the compressive and flexural strength was also assessed. The results of the experiment show that the improvement of the pozzolanic properties of recycled glass by using it as the basis of blended cement is possible. The synergistic effect of the co-grinding of the components was observed. The glass particles were better distributed in the composite and could react with Portland cement hydration products. It positively influenced the values of the material's physical and mechanical parameters.

Effect of barium hydrosilicates on the early hydration rate of Portland cement

We have studied the effect of a barium hydrosilicate-based modifier on the phase composition of Portland cement hydration products. The results demonstrate that the addition of a modifier containing barium hydrosilicates, silicic acid, and calcium carbonate makes it possible to reduce the nucleation rate of crystals of new phases during the induction period of the hydration process, increase alite (3СaO · SiO2) hydration, and reduce the rate of aluminate phase (3CaO · Al2O3) hydration. The use of such a modifier increases the degree of cement hydration and the amount of calcium hydrosilicates and reduces the amount of forming portlandite and ettringite, thereby improving the mechanical properties and durability of the set cement.

The role of Ca(OH)2 in sulfate salt weathering of ordinary concrete

In the present paper, a micro-analysis of sulfate salt weathering of calcium sulfoaluminate (CSA) cement paste and concrete was conducted to offer reference values and to elucidate the sulfate salt weathering of ordinary concrete. The test results showed that Na2SO4 crystals could be clearly identified in CSA cement paste and concrete, causing the failure of the paste and concrete in the evaporation zone. Based on the surface physicochemical theory of crystallization in a pore, a solution film between the pore wall and the salt crystal causes crystal growth and can be formed due to the inert relationship between sulfates and CSA cement hydration products without the effect of Ca(OH)2. However, after the inevitable chemical reaction between the sulfates and hydration products of Portland cement due to the existence of Ca(OH)2, the solution film is not formed, and Na2SO4 crystallization cannot occur in the Portland cement concrete.