Portland Cement Systems Research Articles

Assessment of standard test procedures applied to calcium sulfoaluminate based cements

Cements containing calcium sulfoaluminate (CSA) have reported excellent characteristics at both early and later ages. However, there are a number of studies reporting poor durability when compared with Portland cement (PC). Durability tests are used as an indicator for service life, and thus the viability of a cement system relies on its performance in these tests. Test methods often assume a sufficient maturity based on extensively tested PC systems; however, slower hydrating binder assemblages and variable chemistries can be severely underestimated when tested at the default 28 days. For example, a belitic CSA (BCSA) cement tested at this time will fail to account for later-stage hydration products that can improve the durability of the system. Tests on the durability of BCSA cements beyond 28 days of curing are sparsely covered in the literature, although in each study the results have shown a marked improvement in durability performance – a characteristic paralleled by other slow-hydrating binders such as fly ash composite cements. The use of an equivalent cement hydration/maturity in testing protocols is proposed, which could be considered a baseline for subsequent improvements that can be made with regard to how alternative binder systems are tested. A call to action for the cement community is outlined to (a) understand what tests are actually testing at a chemical level, (b) develop a ‘cure test’ to assess maturity and (c) undertake round-robin testing.

Calcium nitrate as a modifier agent for metakaolin-based geopolymer mortar

Calcium nitrate, that is a calcium source, is generally used as an accelerating agent, antifreezing admixture, and corrosion inhibitor for Portland cement systems. Metakaolin, which is regularly used as a precursor in the production of geopolymers, lacks calcium. This can cause inefficiency of the geopolymerization process and alter the properties of the cementitious product. To overcome this problem, the potential benefits of adding calcium nitrate as an alternative calcium source for the metakaolin geopolymer mortar were investigated. Different ratios of calcium nitrate, ranging from 0.5 % to 10 %, were added into metakaolin geopolymer mortar. Different tests were conducted to know the effect of calcium nitrate on some properties of metakaolin geopolymer specimens, which were cured in either air or water. Advanced analysis methods were leveraged to unlock deeper meaning from the findings. The results indicated that adding calcium nitrate led to increased flowability and shortened setting time. The addition of 0.5–7 % calcium nitrate increased mechanical strength but reduced transport properties, whilst the addition of 10 % calcium nitrate led to adverse effects. The addition of 0.5–7 % calcium nitrate can mitigate the strength deterioration rate resulting from water curing and decrease drying shrinkage. The incorporation of appropriate ratios of calcium nitrate can form calcium silicate hydrate gel and densify the microstructure.

The role of ettringite seeds in enhancing the ultra-early age strength of Portland cement containing aluminum sulfate accelerator

The ultra-early age strength of shotcrete with Portland cement-based materials in various supporting constructions is crucial for safety and engineering efficiency. However, concerns exist about the low strength and uncertain mechanism when using aluminum sulfate, the main component of most-used alkali-free accelerators. This study addresses these concerns by introducing ettringite seeds into the Portland cement system with aluminum sulfate. Significant improvement in ultra-early age compressive strength of mortar, i.e., 242 % at 6 h and 201 % at 8 h, was achieved by mere 1 % seed addition. Analyses of hydration heat, composition and microstructure demonstrate that the ettringite seeds mainly affect the mechanical performance by forming a more prolonged and coarser ettringite skeleton, rather than directly accelerating cement hydration. Such an enhanced skeleton was proved to establish stronger interactions between particles in the Monte Carlo simulations. Additionally, the synergistic effect of the ettringite skeleton and C–S–H gel on ultra-early age strength was also explored. These proposed strengthening mechanisms were verified by the C3S and equivalent CaCO3 systems.

Manufacturing and performance of eco-efficient cementitious blocks for thermal cycling in thermal energy storage

Solar energy is a promising renewable option to provide energy demands in combination with conventional energy sources. However, to enhance the integration of renewable energies into the industrial section, it is necessary to employ thermal energy storage media. Among different thermal energy storage options, concrete has proven to be a very effective sensible thermal energy storage solution. However, its main raw material (i.e., the Portland cement), is the cause of huge CO2 emissions to the environment. This study focuses on the design, manufacture, assembly and experimentation of thermal energy storage blocks made of alternative binders in substitution of Portland cement: i.e., hybrid materials and alkaline activated materials. The thermal energy storage blocks have been thermally cycled, with a charging temperature of 228 °C and a discharging temperature of 30 °C, in order to analyze the operational times and temperatures. The results obtained are very promising and comparable to those of the Portland cement system. Charging times have improved, with the alternative materials achieving temperature increases of up to 4%, while greater stabilization has been achieved during discharge, with the fluid reaching temperatures up to 6% higher than the reference system. These advancements support efficient, sustainable thermal energy storage technologies.

Impact of exposure conditions on alkali-silica reaction in alkali-activated material systems

The influence of different testing methods on alkali-silica reaction (ASR) behavior is a result of the difference in the effect of exposure conditions on it. This study investigated the impact of temperature and the addition of alkali on ASR behavior in an alkali-activated material (AAM) system and compared it with an ordinary Portland cement (OPC) system. The results showed that the ASR in the AAM system was more independent of the exposure conditions than that in the OPC system because of its inherently high alkalinity and dense microstructure. More ASR products with higher Na:Si ratios were evident in the alkali-activated slag (AAS) mortars than in the OPC mortars. The accelerated test conditions developed for OPC systems could be applied to AAM systems. However, owing to the difference in the acceleration effect, comparing the ASR-induced expansion in OPC and AAM systems using the accelerated test method was misleading to some extent. This study contributes to the understanding of the ASR in AAM systems and is of considerable importance for the industrial application of AAMs.

Recycled Concrete Fines as a Supplementary Cementitious Material: Mechanical Performances, Hydration, and Microstructures in Cementitious Systems

Using recycled concrete fines (RFs) as a supplementary cementitious material in blended cement systems offers potential benefits for the construction industry. This study investigated the mechanical properties, hydration development, and microstructural evolutions of blended Portland cement systems incorporating different particle-size distributions of untreated RFs. The results highlighted that finer RFs improved the compressive strength of mortar and influenced hydration by promoting monocarbonate formation. The incorporation of RFs optimizes the pore structure in the early stage but increases porosity. RFs affected the distribution of capillary pores and created a rougher and more complex surface compared to inert mineral admixtures. Furthermore, the particle size of RFs impacted the fractal dimension of multi-scale pore sizes.

Potential applicability of calcium phosphate modified portland cement paste for geologic sequestration of CO2

In order to increase the integrity of the wellbore which is used to prevent the leakage of supercritical CO2, it is necessary to develop a concrete that is strongly resistant to carbonation. In an environment where the concentration of CO2 is exceptionally high, Ca2+ concentration in portland cement concrete drops significantly due to the rapid consumption of calcium hydroxide, which decreases the stability of the calcium silicate hydrate. In this work, it is hypothesized that if fairly large quantity of the hydration product becomes more thermodynamically stable than calcite, the damage caused by rapid carbonation will certainly be minimized. For this purpose, portland cement system was modified by monocalcium, dicalcium and tricalcium phosphates to produce hydroxyapatite in portland cement paste. According to the experimental results, addition of calcium phosphate produced hydroxyapatite. Among three different calcium phosphates, monocalcium phosphate showed the most significant impact on hydration. It caused faster stiffening and delayed calcium silicate hydration. Although cement pastes modified by calcium phosphates showed less compressive strength than plain cement paste, they showed an excellent durability after exposure to supercritical CO2. It is clear from the results that the potential applicability of calcium phosphate modification in portland cement for geologic sequestration of CO2 was successfully proven.

THE EFFECT OF CRUMB RUBBER ON THE PROPERTIES OF MODIFIED PORTLAND CEMENT SYSTEMS

The use of rubber crumb from used tires in concrete as a partial replacement of natural aggregates is an ecologically oriented direction of their utilization. When rubber crumb was added to Portland cement, a decrease in strength was observed. Modification of rubber-containing Portland cement systems with a complex organic and mineral additive makes it possible to compensate for the loss of compressive strength and provide increased impact strength. Samples without rubber show high strength but are characterized by fragility and sudden destruction of the material. Samples containing rubber show relatively low mechanical resistance but also exhibit elastic behavior where slow fragmentation and slow failure of the material after crack initiation are observed. They also are characterized by additional load resistance after reaching the failure stress, which is associated with the bridging effect of rubber particles.

How does carbonation of alkali-activated slag and Portland cement systems impact steel corrosion differently?

Carbonation of cementitious materials, associated with neutralization of pore solution, is one of the prevalent reasons for inducing corrosion of steel in concrete. Compared with ordinary Portland cement (OPC) concrete, the poorer carbonation resistance of alkali-activated slag (AAS) concrete leads to serious durability concerns of a higher risk of steel corrosion. This work investigates the corrosion behaviors of steel embedded in intact and carbonated AAS and OPC mortars exposed to various relative humidity conditions, with the aim of fostering a better understanding of how carbonation impacts steel corrosion differently in these two cementitious systems. The results show that uncarbonated AAS mortars have better protective ability against corrosion than OPC counterparts; however, poorer performance after complete carbonation. It is mainly attributed to the combined effect of severe deterioration and coarsening of pore structure and increased ratio of chloride ion concentration to hydroxide ion concentration ([Cl−]/[OH−]) in pore solution, resulted from the consumption of hydroxide ions and release of bound chloride after carbonation. Besides, the different shifts of R-C (material resistivity versus corrosion rate) relationship lines in AAS and OPC mortars after carbonation are observed, which is ascribed to the different compositional and microstructural evolutions induced by carbonation in these two cementitious systems.

The Role of Chemical Activation in Strengthening Iron Ore Tailings Supplementary Cementitious Materials

The preparation of iron ore tailings (IOTs) into supplementary cementitious materials (SCMs) is an effective approach to achieve value-added utilization of industrial solid waste. This study systematically investigates the hydration pattern and strength development of Portland cement systems with the incorporation of IOTs, steel slag (SS), granulated blast-furnace slag (GBFS), and fly ash (FA) under the action of different chemical additives. The hydration products, and microstructure and pore structure of the SCMs are analyzed using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and mercury intrusion porosimetry. The findings of this study demonstrate that chemical activation plays a significant role in the strength development of SCMs. Among the five chemical activators tested, Triethanolamine (TEA) had the greatest influence on mechanical properties. The maximum compressive strength of the SCMs at 28 days was 42.9 MPa at a dosage of 1%. Specifically, the addition of TEA promotes volcanic ash reactions, and the high fineness of SCM provides nucleation sites for hydration products. Interactions between the volcanic ash reaction and the complexation reaction of TEA have a positive effect on compressive strength development. This research expands the potential for IOTs SCMs through chemical activation methods for value-added applications.

Research on the strength reduction mechanism of Cement Kiln Dust (CKD) – Portland cement systems from macroscale and nanoscale

Cement kiln dust (CKD) is a solid waste produced by the thermal decomposition of materials during the production of cement clinker. Theoretically, CKD can potentially be utilized to replace cement materials, which can reduce the expend for natural resources. However, the detailed mechanism of CKD on the source of strength reduction from macroscale and nanoscale is still unclear. This study focus on revealing the strength reduction mechanism of CKD-Portland cement. The results show that the strength reduction is dominated by the sulfate composition contents, which is not relative with the generation of lower elastic modulus C-S-H. And the higher ratio of S/Si is not conducive to enhancing strength. At the microscale, both the crystalline hydrates contend and the corresponding morphology are depended on the CKD dosages. And at the nanoscale, the generated C-S-H is characterized as a stacking structure. The average elastic modulus of generated C-S-H is 33.0 GPa. The relative contents of VLD, LD, HD and UHD C-S-H of the CKD-Portland samples are 4.7%, 22.0%, 37.9% and 35.2%, respectively. Furthermore, the CKD promoted the reaction rate and accelerated the hydration process. This study provides valuable insights into the application of CKD in cement-based material.

Corrosion resistance of cement-based materials with sugarcane bagasse ash-metakaolin-Portland cement binder under carbonic acid water environment

This paper investigated the corrosion process of sugarcane bagasse ash (SCBA)-metakaolin (MK)-Portland cement (PC) system under carbonic acid water environment. The phases of cement paste before and after corrosion and microstructure were analyzed by X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy and scanning electron microscope. The results showed that the addition of SCBA to mortar does not significantly enhance overall strength or reduce corrosion depth, whereas MK exhibits superior strength (up to 13.1% higher than SCBA) and lower corrosion depth (up to 69.6% lower than SCBA after 90 days of corrosion). Furthermore, SCBA is more conducive to maintaining strength over time compared with MK. When both MK and SCBA are used in mortar, particularly with a MK content exceeding 15% and an SCBA content below 5%, the optimal corrosion resistance effectiveness can be achieved. This is attributed to the synergistic pozzolanic effect of MK and the filling effect of SCBA.

Features of Hardening and Utilization of Modern Cement Compositions with Nanomodifying Additives For Repair And Restoration Works

The paper presents the results of a study of the peculiarities of structure formation when adding complex silica-carbonate nanomodifying additives to Portland cement. The conducted research indicates that the modification of cement systems with complex organosilicate-carbonate additives leads to the directed formation of low-alkali hydro-silicate phases such as scawtite. These phases not only contribute to strength synthesis but also influence the micro-reinforcement characteristics of the cement matrix and the rheological properties of concrete mixes. The obtained high-strength matrices based on Portland cement systems modified with these additives can serve as the foundation for restoration and repair plaster and concrete materials used in emergency and urgent conservation work on cultural heritage sites during times of military conflict.

Carbonation study of new calcium aluminate cement-based CO2 injection well sealants

In injection-well carbon storage projects, the degradation of Portland cement under harsh CO2 conditions is a primary concern. This study introduces novel CO2-resistant calcium aluminate cement (CAC) systems with addition of rubber latex and hollow glass microspheres which are added to the system to enhance the set cement resistance to CO2 corrosion and in the same time to optimize it for the application in a wide variety of well conditions. After exposure to near supercritical CO2 conditions (100 °C, 7 MPa) these systems exhibited enhanced compressive strength and reduced porosity compared with conventional Portland cement (PC) system, especially the one without latex. By subjecting degradation depth-resolved samples to thermogravimetry (TG) and X-ray diffraction (XRD) techniques, coupled with scanning electron microscopy (SEM), the study scrutinized alterations in microstructural properties. This methodological approach unveiled a profound grasp of carbonation mechanisms. Confirmed through TG and XRD analyses, the considerable reduction in carbonation establishes CAC as a compelling choice for CO2-resistant sealing within injection-well CO2 storage endeavors.

Recycling of Aluminosilicate-Based Solid Wastes through Alkali-Activation: Preparation, Characterization, and Challenges

Recycling aluminosilicate-based solid wastes is imperative to realize the sustainable development of constructions. By using alkali activation technology, aluminosilicate-based solid wastes, such as furnace slag, fly ash, red mud, and most of the bio-ashes, can be turned into alternative binder materials to Portland cement to reduce the carbon footprint of the construction and maintenance activities of concrete structures. In this paper, the chemistry involved in the formation of alkali-activated materials (AAMs) and the influential factors of their properties are briefly reviewed. The commonly used methods, including X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TG), nuclear magnetic resonance spectroscopy (NMR), and X-ray pair distribution function technology, to characterize the microstructure of AAMs are introduced. Typical characterization results of AAMs are shown and the limitations of each method are discussed. The main challenges, such as shrinkage, creep, efflorescence, carbonation, alkali–silica reaction, and chloride ingress, to conquer for a wider application of AAMs are reviewed. It is shown that several performances of AAMs under certain circumstances seem to be less satisfactory than traditional portland cement systems. Existing strategies to improve these performances are reviewed, and recommendations for future studies are given.

Impact of triethanolamine on the hydration of Portland cement in the presence of high pozzolanic activity supplementary cementitious materials

Triethanolamine (TEA) is a widely employed cement accelerator that has been demonstrated to have a favorable impact on the early strength of cement at moderate dosing levels, while having a slight or negative impact on the later strength. This study systematically investigates the hydration pattern and strength development of Portland cement systems with the incorporation of fly ash microspheres and silica fume at a dosage of 0.02 % triethanolamine. The results proved that the addition of TEA had a positive impact on the early strength of the pure Portland cement system, while the later strength was reduced. However, the presence of high pozzolanic activity supplementary cementitious materials (SCMs) altered this reduction and even reversed it, resulting in an increase in strength. Specifically, TEA inhibits the crystallization nucleation growth of hydration products through complexation, resulting in the inhibition of the hydration of silicate minerals. The nucleation effect of silica fume, however, eliminates this inhibition and promotes the hydration of all minerals. Moreover, the presence of SCMs leads to the formation of more amorphous calcium hydroxide (CH) due to the demand of pozzolanic reaction, and the addition of TEA promotes the formation of amorphous CH, effectively lowering the reaction threshold of the pozzolanic reaction and facilitating it. The results confirm that the interaction of the complexation reaction of TEA with the pozzolanic reaction provides a beneficial complement to cement strength development.

Effects of Bogues Compounds and Particle Size Distribution on the Physico-mechanical and Microstructural Properties of Portland Cement System

Effects of Bogues Compounds and Particle Size Distribution on the Physico-mechanical and Microstructural Properties of Portland Cement System

RETRACTED: Effects of submicron CaAl–NO3 layered double hydroxide on the early and mature age properties of calcium sulfoaluminate and Portland cement systems

Layered double hydroxide (LDH) is reported to improve durability of concretes, primarily due to its ability to exchange anionic species, including chloride, which is implicated in corrosion-driven durability issues. However, there is no comprehensive study investigating the effect of LDH on the properties of different cement systems at both early and mature ages. In this study, the early age and mature age properties of Portland cement (OPC) and calcium sulfoaluminate (CSA) cement pastes seeded with submicron-sized calcium aluminum-NO3 LDH (CaAl-NO3 LDH) were investigated. The effects of the 1–5%mass dosage of LDH on the hydration of both cement systems were characterized by rheology, isothermal calorimetry, porosimetry, compressive strength tests, thermogravimetric analysis, and x-ray diffraction. Time-dependent rheology results indicate that CaAl-NO3 LDH seeding enhanced the buildability of cement pastes, as evidenced by increased plasticity loss, hardening, and yield stress. While LDH seeding accelerated hydration kinetics for both CSA and OPC pastes, interestingly, the OPC exhibited reduced heat release, suggesting potential applications of LDH as heat sink in various areas, including building in hot climates, reducing heat and crack-propensity in mass concrete placements, and 3D-printed OPC-based concretes. Although LDH slightly decreased compressive strengths at both 1d and 28d, its primary role was to expedite the hydration process without enhancing the microstructure or strength of the final product.

Alkali-Activated Slag Coatings for Fire Protection of OPC Concrete

During a fire, ordinary Portland cement (OPC) systems lose their mechanical properties. For this reason, it is important to find a way to protect it. This study suggested alternative uses of slag and phosphogypsum to produce coatings for fire-resistant applications. Five compositions of 10 mm thick alkali-activated slag coatings were investigated. In these compositions, different amounts of phosphogypsum (1%, 3%, 5%, 7%, and 10%) were used. In the first stage of this study, the residual compressive strength of samples with the coatings based on alkali-activated slag was compared to the results of OPC concrete samples without coatings. The experimental results showed that a higher residual compressive strength of 33.2–47.3 MPa OPC concrete was achieved for the samples with coatings. Meanwhile, the residual compressive strength of the uncoated samples was 32.37 MPa. In the second stage, OPC concrete samples were reinforced with fiberglass polymer (FRP) rods, and they had a similar positive effect on alkali-activated coatings. After exposure to higher temperatures, the pullout tests of the glass FRP bars showed that the adhesion strength was (9.44 MPa) 43.9% higher for the samples with coatings compared to the samples without coatings (6.56 MPa). Therefore, a higher bond strength can be maintained between concrete and FRP bars. Alkali-activated slag with 3% phosphogypsum can be used for the production of fire-resistant coating. These coatings could protect OPC concrete and reinforced concrete with glass FRP bars from fire.

Effect of carbonation on the corrosion behavior of steel rebar embedded in magnesium phosphate cement

Magnesium Potassium Phosphate Cement (MKPC) as a protective binder for steel rebars has been well-established. However, corrosion performance of steel rebars in MKPC subjected to carbonation is still unknown. This investigation aimed at revealing the impact and mechanism of carbonation on corrosion performance of steel rebars in MKPC using electrochemical techniques and surface analyses. The findings indicate that, unlike Portland cement (PC) system, carbonation positively influences corrosion performance of steel rebars when embedded in MKPC, as demonstrated by comparable (M/P = 7) or even higher (M/P = 12) corrosion resistance values. Under carbonation, the ingressive CO2 reacts with Mg-bearing phases in MKPC to form nesquehonite with a higher pH, while the MgO still keep supersaturated. The resultant increase in pH facilitates formation of ferrous oxide and iron phosphate/borate within oxide film developed on steel surface, which enhances protective capability of oxide film and consequently improves the corrosion resistance of the steel rebars.