High Initial Strength Portland Cement Research Articles

Clinker Portland with iron ore tailing and its characterization by integrated laboratory methods

The large volume accumulation of iron ore tailings (IOT) in Brazil poses significant risks of accidents, highlighting the need for strategies for their recycling. The Brazilian's IOT possesses mainly iron oxide content (HI-IOT) and can be used as raw materials alternatives in clinker production. Based on a fixed lime saturation factor (LSF = 0.96), we incorporated 5 to 10 wt% of HI-IOT in the raw meal to produce Portland clinkers. The mineralogical phases (alite, belite, aluminate, and ferrite) were evaluated by quantitative X-ray diffraction. Optimal results were obtained with 7.5 wt% of HI-IOT in the clinker Portland, i.e., approximately 32 %wt. of clay substitution. The mechanical strength evolution was evaluated by a reduced-size test and obtained compressive strength of 34.8 MPa at 3 days-age, 54.10 MPa at 7 days-age, and 71.20 MPa at 28-days values compatible with standardized high initial strength Portland cement. By monitoring the complete hydration process using TG/DTG and assessing the volumetric composition over time, valuable insights were gained regarding the potential application of these Portland cements at an industrial scale.

The role of calcium silicates and quicklime on the reactivity of rehydrated cements

Construction and demolition waste recycling is mandatory in the context of circular economy. Specifically, applications for the cementitious waste fines are less discussed in scientific literature and barely implemented. Apart from the use of cementitious waste fines as raw materials for clinker production, thermal treatment by the decomposition of fines at temperatures lower than 600 °C has been explored to produce an alternative binder implying under this limit in low CO2 emissions during production. However, there are doubts if its reactivity results from the hydration from residual calcium silicates, and quicklime (CaO) eventually formed after the thermal treatment. This paper investigated quantitively the contributions of calcium silicates and quicklime by thermogravimetry (TG) and quantitative X-ray diffraction (QXRD) on the reactivity of the rehydrated cements. After hydration of the high initial strength Portland cement, only 5% (g/g) of calcium silicates remained, mostly larnite. After dehydration at 500 °C, only 6% (g/g) of quicklime was formed due to the decomposition of portlandite. Intermediate silicates increased in function of temperature of dehydration until 500 °C, but the contents were lower than 18%-g/g. Those phases can explain partially the heat released during rehydration. The heat seemed to be also related to the chemically bound water in the reformation of amorphous C-S-H. In fact, for a fixed water/cement ratio, the increase of chemically bound water explained both, the increase of heat released and the compressive strength of the rehydrated cements. This supports our finding that the calcium silicates or quicklime are not the only responsible for the reactivity of this binder.

Leaching assessment of cemented bauxite tailings through wetting and drying cycles of durability test.

Disposal of mine tailings can cause negative environmental effects by releasing contaminants to surface and underground water. Alkali activation is a promising technique for immobilizing metals in stabilization/solidification of these wastes. This study evaluates the leaching behavior of cemented bauxite tailings (BT) submitted to weathering conditions. The alkali-activated binder was composed of sugar cane bagasse ash, carbide lime, and sodium hydroxide solution. Comparisons of the durability and leaching behavior of BT stabilized with alkali-activated binder and high initial strength Portland cement were performed. The durability results for alkali-activated were similar to the Portland cement, showing an average difference of 16%. Portland cement showed favorable results in the encapsulation of heavy metals like Cd and Hg, while the alkali-activated cement on Al, Cr, and Se. For Ba, Fe, Mn, and Zn immobilization, both types of cement presented an equal performance. The durability and leaching behavior of stabilized bauxite tailings is governed by the cement content and porosity of the blends, as well as their pH.

Stabilization of gold mining tailings with alkali-activated carbide lime and sugarcane bagasse ash

Recent tailings dam failures have attracted special attention to the mining sector. These incidents pressured the mining industry to develop more secure and sustainable practices. Geotechnical techniques, such as soil stabilization with ordinary Portland cement (OPC), have been explored as alternatives to this problem. However, OPC production is associated with high energy consumption, exploration of natural resources, and greenhouse gases emission. Thus, alternative materials to OPC, with lower environmental impacts and similar mechanical performance, are growing in interest for stabilization techniques. The present study describes the mechanical behavior of gold tailings stabilized with alkali-activated carbide lime and sugarcane bagasse ash. As a control group, the gold tailings were also stabilized with high initial strength Portland cement (type III). The specimens were tested regarding their unconfined compressive strength, stiffness, and durability. All results were correlated with the porosity/binder index to create a rational dosage methodology for the tailings-cement mixtures. Results have shown that Portland cement mixtures resulted in more expressive strength, stiffness, and durability results when compared to the alkali-activated cement. Nevertheless, the alternative cement was also able to improve the mechanical behavior of the gold tailings. Reduction in porosity and increase in cement content led to the improvement of the mechanical behavior of all specimens. A direct correlation was established between strength, stiffness, and durability. The porosity/binder index was shown to be a viable dosage method to predict the mechanical behavior of stabilized gold tailings, allowing the unification of the results in a single relation, replacing trial and error conventional strategies.

Evaluation of compressive strength of concrete with metakaolin using different levelling techniques

The partial replacement of cement by mineral additions such as metakaolin has been widely applied in the production of high-strength and durable concretes due to the pozzolanic action, allowing a reduction in the consumption of cement. Tests are performed to determine the mechanical properties of these materials, such as compressive strength, for which there are different levelling techniques of specimens, such as sulphur and neoprene, indicated for different resistance classes. The present study aimed to characterize the behaviour, in the hardened state, of concrete produced with high initial strength Portland cement (CPV-ARI) and metakaolin and evaluate the different levelling methods. Three groups of samples dosed by the IPT-EPUSP method, with mix designs of 1:3, 1:5, and 1:6, and replacements of 8 and 10% of cement by metakaolin, were subjected to compressive strength test, at the ages of 28 days, with levelling by neoprene, and 90 days, with levelling by sulphur. It was observed an increase in strength with addition of metakaolin at both ages. Comparing the results in the two ages, it was verified an increase in strength for the mix designs 1:5 and 1:6 and a reduction for the mix design 1:3. Such fact can be explained by the high strengths achieved by this mix design. As the levelling method used was sulphur, it is confirmed the imprecision of results for strengths above 50 MPa with this technique.

Early carbonation curing effects on the microstructure of high initial strength Portland cement pastes

The microstructure of high early strength and sulfate-resistant Portland cement carbonated pastes at two different durations of carbonation (1 h and 24 h) was analysed under the best conditions for carbon dioxide capture as indicated in previous studies by the authors. The aim was to determine, by means of X-ray diffraction analysis, nuclear magnetic resonance spectroscopy and scanning electron microscopy, how different carbonation times affect the microstructure of the pastes and to explain their respective related mechanical and porosity properties. The microstructure of the reference paste was homogeneous. The 1 h carbonated paste showed a more porous region near its external surface, surrounding a much higher inner non-porous homogeneous phase, while the 24 h carbonated specimen showed a single and more porous phase. The longer the carbonation time, the higher was the microstructural porosity of the carbonated regions and the higher the condensed silicate structure of the matrix, as characterised by morphology modifications. The resultant mechanical and physical properties of the pastes were affected by these chemical changes.

Effect of early age curing carbonation on the mechanical properties and durability of high initial strength Portland cement and lime-pozolan composites reinforced with long sisal fibres

This paper presents the results of a study about the mechanical behaviour, before and after aging, of two cement-based composites reinforced with long sisal fibres cured at early age in a CO2 environment. After curing, samples of both composite systems were submitted to wetting and drying cycles to accelerate the aging of the materials allowing the evaluating of the efficiency of the CO2 treatment. Besides promoting CO2 capture, the used cure also allowed the increase in the durability of the sisal fibre-cement based composites by the Calcium Hydroxide (CH) consumption and pH decrease promoted by the carbonation reactions. The lime-pozzolanic material composite was also treated with CO2 at early stages of formation, with the carbonation and pozzolanic reactions acting simultaneously to deplete the Ca(OH)2 thus improving its durability. Four-point bending test, thermogravimetry analysis of the matrix and SEM analysis of the fibres were done before and after aging to study the durability mechanisms of the composites. The obtained results showed that the CH free cement-based composite containing metakaolin and fly ash presented the best mechanical behaviour before and after accelerated aging. The early age carbonation of the lime-pozolan composites improved its mechanical response, before and after accelerated aging, when compared with the non-carbonated samples. The thermogravimetry test showed that the increase of the carbonation time of the reference Portland cement-based composite consumed the CSH, compromising the ductility and strain capacity of this composite family after aging. The SEM pictures showed petrified fibre effect by the migration of hydrated products after 10 and 20 cycles of ageing for this composite system.

Influence of preloading-induced microcracking on the durability of concrete produced with different types of cement

As many concrete structures present premature degradation, large environmental and financial impacts are associated with repairing. It is essential, therefore, to understand mechanical and durability performance of concrete in different conditions of use. This study investigated the chloride penetration resistance of microcracked concretes after being exposed to early loading. So, cylindrical test specimens were prepared with two Brazilian cements, a high initial strength Portland cement and a pozzolanic one, with a water/cement ratio of 0.50. At the age of 3 days, some of the specimens were subjected to a load of 75% of their ultimate compressive strength while reference ones were not preloaded. All specimens were cured by immersion in water tanks for 3, 7, 28 and 91 days. After these periods, preloaded and reference specimens were tested in accordance with chloride penetration resistance (ASTM C1202/12). The best results were observed in the reference samples for both cement types. It was observed a significant reduction in chloride penetration for longer curing times in preloaded and reference specimens due to self-healing. Differences between preloaded and reference specimens were identified, at ages of 3 and 91 days, using scanning electron microscopy and electromagnetic radiation spectra, a non-destructive and low-cost remote sensing technique.

A study of CO2 capture by high initial strength Portland cement pastes at early curing stages by new non-conventional thermogravimetry and non-conventional differential thermal analysis

Although the literature presents intensive studies based on monitoring cement hydration in adiabatic and semi-adiabatic environments, such as non-conventional differential thermal analysis (NCDTA) systems, studies of cement hydration in controlled climatic chambers are very rare. Using three W/C ratios (0.5, 0.6 and 0.7) and three relative humidity conditions (60, 80 and 100%) at 25 °C, the authors analyzed in real time the evolution of cement hydration reaction during the first 24 h in an environmental-controlled chamber. The main objective of this paper is to present two new developed systems of NCDTA (NNCDTA) and non-conventional TG and to show, using high-strength sulfate-resistant Portland cement pastes in a controlled chamber as application examples, how the developed systems measure on real time the thermal effects and the mass changes that occur during hydration and carbonation reactions. The captured CO2 mass can be quantified as it occurs by carbonation curves. The results are in agreement with the mechanical and structural properties of the used pastes and with their TG/DTG data, after being processed by different operational conditions. Carbonation for 24 h alters significantly the cement hydrated paste composition, resulting in final poor mechanical resistance properties. However, carbonation for 1 h, in specific conditions, enhances them when compared to a non-carbonated reference paste, due to a final higher content of silica and alumina hydrated phases and to a lower mass ratio between that of their combined water and their total mass as well.

Hydration and Dehydration of High Initial Strength Portland Cement Type CP V - ARI

It is known that the hydration of cement paste is influenced by a variety of factors, it is also known that some hydration products are gradually dehydrated at elevated temperatures. In doing so, different author studied the dehydration of hydrated cement pastes under different condition. In this work, samples of Hydrated Cement Paste (HCP) were prepared from Portland cement of high initial strength (CP V-ARI) with a water/cement ratio of 0.5. The morphological changes during hydration and dehydration by subsequent heat-treatments were analyzed by X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). Thermal Gravimetric Analysis (TGA) was used to study the thermal stability of the HCP. Dehydrated cement powder samples (DCP) were obtained heat treating samples of HCP at 300, 500, 700 and 900°C. After 7 days of curing HCP samples exhibited no significant changes in its structure. HCP dehydrated at 500°C showed the absence of Ca (OH)2 and calcium silicate hydrate. At 700°C the formation of β-2CaO.SiO2, 3CaO.SiO2 and CaO is observed. During heat treatment at 900°C the HCP revealed a significant mass loss of 36%.

The effects of the early carbonation curing on the mechanical and porosity properties of high initial strength Portland cement pastes

Mechanical and porosity related properties of high initial strength sulfate resistant Portland cement (HS SR PC) pastes subjected to early age carbonation curing were investigated. This work presents the characterization through mechanical properties, of carbonated HS SR PC pastes and of non-carbonated references. They were treated at two different times of carbonation (1h and 24h), at the best conditions of capturing, previously determined by the authors. The mechanical properties were characterized by compressive strength, tensile strength by diametrical compression, elastic modulus and Poisson’s coefficient. It was found that 1h of carbonation improved the mechanical properties, while the increase of carbonation time to 24h, decreased significantly the same properties in relation to the reference specimens. The porosity related properties were characterized by total absorption, absorption by capillarity, gas permeability, and mercury intrusion porosity. It was noticed that the increase of the carbonation time from 1h to 24h, increased substantially the absorption properties. Despite the mechanical properties of the 1h carbonated paste were better than those of the reference, the absorbed water content of the carbonated specimen was slightly higher than that of the reference.

Mechanical and Physical Properties of Early Carbonated High Initial Strength Portland Cement Pastes

After submitted to early age carbonation curing, mechanical and physical properties of high initial strength sulfate resistant Portland cement (HS SR PC) pastes were investigated, which were compared to those of non-carbonated reference pastes. Carbonation was performed for 1 and 24 hours, at the best conditions of CO2capturing, previously determined by the authors. Despite the compressive strength and elastic modulus of the 1h carbonated pastes were slightly higher than those of the reference pastes, their absorbed water content and porosity was slightly higher than that of the reference. In the case of 24h carbonation, its compressive strength decreases significantly because of its much higher porosity, although the new solid carbonated calcium silicate phase presents a much higher specific mass than those of the solid phases of the 1 hour and non-carbonated pastes.

CO2 sequestration by high initial strength Portland cement pastes

During the formation of pastes, mortar and concretes have been used to capture CO2. This work presents a methodology to estimate the carbon dioxide (CO2) sequestered by high strength and sulfate-resistant Portland cement pastes during their early stages of hydration, by Thermogravimetry and Derivative Thermogravimetry. Water to cement ratio equal to 0.50 and 0.70 were evaluated and the captured CO2 amount was determined through TG/DTG curve data on initial cement mass basis, obtained during accelerated carbonation from the fluid state and accelerated carbonation after a first hydration process. The experiments were performed in a controlled chamber, maintaining the CO2 content at 20 vol % and the temperature at 25 °C, at different relative humidity (RH) (60 and 80 %) ambient. The procedure allows one to estimate the amount of CO2 sequestered by the initial cement mass of a given volume of paste, as well as to evaluate the RH and W/C ratio influence on the amount of hydrated formed products, mainly on the Ca(OH)2, important for CO2 fixation.

Early stages hydration of high initial strength Portland cement

Early stages hydration of high initial strength Portland cement

Early stages hydration of high initial strength Portland cement

Thermogravimetry (TG) and derivative ther- mogravimetry (DTG) were used to analyze the early stages of hydration of a high-initial strength and sulphate resistant Portland cement (HS SR PC) within the first 24 h of set- ting. The water/cement (W/C) mass ratios used to prepare the pastes were 0.35, 0.45, and 0.55. The hydration behavior of the pastes was analyzed through TG and DTG curves obtained after different hydration times on calcined cement mass basis to have a same composition basis to compare the data. The influence of the W/C ratio on the kinetics of the hydration process was done through the quantitative analysis of the combined water of the main hydration products formed in each case. TG and DTG curves data calculated on calcined mass basis of all the results were converted to initial cement mass basis to have an easier way to analyze the influence of the W/C ratio on the free and combined water of the different main hydrated phases. The gypsum content of the pastes was totally consumed in 8 h for all cases. A significant part of the hydration process occurs within the first 14 h of setting and at 24 h the highest hydration degree, indicated by the respective content of formed calcium hydroxide, occurs in the case of the highest initial water content of the paste.