High Strength Portland Cement Research Articles

Enhancement of oriented cement-bonded boards' properties through CO2 curing.

This study investigates the effects of CO2 curing on oriented cement-bonded boards. The boards comprised 35% and 45% (by mass) of strand-type particles of Eucalyptus spp. (8 × 2 × 0.1cm) and 65% and 55% (by mass) of early high-strength Portland cement. To fabricate the boards, three layers of strands were arranged perpendicular to the previous layer, aiming for a target density of 1250kg/m3, and the dimensions of the boards were 40 × 40 × 1cm. The oriented cement-bonded boards underwent three different curing conditions: control, CO2 curing for 6h, and 12h, followed by curing in a saturated environment until the 28th day. The results indicated that CO2 curing increased the CaCO3 content in the boards, particularly when the curing period was longer (12h). The physical and mechanical performance of the CO2-cured boards surpassed that of the control boards, with the modulus of rupture (MOR) increasing by 80% (6h) and 84% (12h) compared to the control. Scanning electron microscope investigations revealed that CO2 curing produced a denser matrix, leading to an improved bond between the strands and the matrix, resulting in enhanced technical performance. Based on these findings, this study suggests that CO2 curing can enhance the physical and mechanical properties of oriented cement-bonded boards, and a longer curing time (12h) yielded superior performance.

Investigation of Impact Resistance of High-Strength Portland Cement Concrete Containing Steel Fibers.

Impact resistance of Portland cement concrete (PCC) is an essential property in various applications of PCC, such as industrial floors, hydraulic structures, and explosion-proof structures. Steel-fiber-fortified high-strength concrete testing was completed using a drop-weight impact assessment for impact strength. One mix was used to manufacture 320 concrete disc specimens cured in both humid and dry conditions. In addition, 30 cubic and 30 cylindrical specimens were used to evaluate the compressive and indirect tensile strengths. Steel fibers with hooked ends of lengths of 20, 30, and 50 mm were used in the concrete mixtures. Data on material strength were collected from impact testing, including the number of post-first-crack blows (INPBs), first-crack strength, and failure strength. Findings from the results concluded that all the steel fibers improved the mechanical properties of concrete. However, hooked steel fibers were more effective than crimped steel fibers in increasing impact strength, even with a smaller length-to-diameter ratio. Concrete samples containing hybrid fibers (hooked + crimped) also had lower compressive strength than the other fibers. Comparisons and analogies drawn between the test results and the static analyses (Kolmogorov–Smirnov and Kruskal–Wallis) show that the p-value of the analyses indicates a more normal distribution for curing in a humid environment. A significant difference was also observed between the energy absorptions of the reinforced mixtures into steel fibers.

Flexural behavior evaluation of repaired high strength geopolymer concrete

CO2 is released during the manufacture of ordinary Portland cement (OPC). The utilization of wastes and byproducts in concrete can lead to new sustainable constructions. To replace OPC in high-strength Portland cement concrete (HSPC), ground granulated blast furnace slag (GGBS) is utilized. GGBS is a by-product of the blast furnace used for iron manufacturing. It has a high silicate gel content and is used to produce good concrete. This paper investigates the load-deformation behavior of high-strength reinforced geopolymer concrete (HSGC) beams that were tested in flexure after being repaired. Six beams were placed using HSGC and HSPC. The original beams were tested, and deflections were measured. Specimens were tested under static stresses, then repaired with epoxy resin injection and re-tested for flexural strength. For both the original and repaired beams, load versus deflection graphs were recorded. Maximum deflection, ultimate load, cracking load, and crack pattern were all determined. The findings suggest that the restored HSGC beams' strength is equivalent to that of the original beams. The strength of the beam has been recovered. The cracks do not re-open after retesting, instead, new nearby cracks developed. The repaired beams showed superior flexural behavior and greater ductility than the original beams.

Curing Effect on Durability of Cement Mortar with GGBS: Experimental and Numerical Study.

In this paper, supplementary cementitious materials are used as a substitute for cement to decrease carbon dioxide emissions. A by-product of the iron manufacturing industry, ground granulated blast-furnace slag (GGBS), known to improve some performance characteristics of concrete, is used as an effective cement replacement to manufacture mortar samples. Here, the influence of curing conditions on the durability of samples including various amounts of GGBS is investigated experimentally and numerically. Twelve high-strength Portland cement CEM I 52.5 N samples were prepared, in which 0%, 45%, 60%, and 80% of cement were substituted by GGBS. In addition, three curing conditions (standard, dry, and cold curing) were applied to the samples. Durability aspects were studied through porosity, permeability, and water absorption. Experimental results indicate that samples cured in standard conditions gave the best performance in comparison to other curing conditions. Furthermore, samples incorporating of GGBS have superior durability properties. Permeability and water absorption were improved by and , respectively, compared to the reference sample. Thereafter, data from capillary suction experiments were used to numerically determine the hydraulic properties based on a Bayesian inversion approach, namely the Markov Chain Monte Carlo method. Finally, the developed numerical model accurately estimates the hydraulic characteristics of mortar samples and greatly matches the measured water inflow over time through the samples.

Strain Hardening of Polypropylene Microfiber Reinforced Composite Based on Alkali-Activated Slag Matrix.

A comparative study of the fracture features, strength and deformation properties of pseudo strain-hardening composites based on alkali-activated slag and Portland cement matrices with polypropylene microfiber was carried out. Correlations between their compositions and characteristics of stress–strain diagrams under tension in bending with an additional determination of acoustic emission parameters were determined. An average strength alkali-activated slag matrix with compressive strength of 40 MPa and a high-strength Portland cement matrix with compressive strength of 70 MPa were used. The matrix compositions were selected for high filling the composites with polypropylene microfiber in the amount of 5%-vol. and 3.5%-vol. ensuring the workability at the low water-to-binder ratios of 0.22 and 0.3 for Portland cement and alkali-activated slag matrices, respectively. Deformation diagrams were obtained for all studied compositions. Peaks in the number of acoustic signals in alkali-activated slag composites were observed only in the strain-softening zone. Graphs of dependence of the rate of acoustic events occurrence in samples from the start of the test experimentally prove that this method of non-destructive testing can be used to monitor structures based on strain-hardening composites.

Citric Acid Effect in High early Type Portland Cement Pastes and Mortars

The influence of citric acid in the properties of high strength Portland cement pastes and mortars, both in fresh and hardened condition, was evaluated. The content of citric acid varied from 0 to 0.8 wt%. Tests were carried out in cement pastes to determine the water required for normal consistency and initial and final setting times. Mortars cements were tested to define bulk density, consistency index, air content in the fresh condition and compressive strength after 7, 14, and 28 days. Analysis by XRD was also performed. The results showed that the use of citric acid as a retardant additive is a viable procedure, because it increased the mechanical strength after 14 days and improved the mortar workability.

Effect of low-pressure microwave-accelerated curing on the drying shrinkage and water permeability of Portland cement pastes

The effect of microwave-accelerated curing on the permeability and drying shrinkage of Portland cement pastes was analyzed. Microwave-based curing is one of the technologies recommended for improving the drying shrinkage and permeability of cement pastes owing to its techno-economic advantages. Low-pressure accelerated microwave heating, also called accelerated dewatering, is an innovative technique that enhances the properties of Portland cement pastes such as high-strength Portland cement pastes. In this study, the effects of this improvement were investigated, including the impact of the pressure on the feed direction, microwave cavity, and different cement paste specimens for each treatment batch. Examination of the initial state of this treatment established the following. First, to avoid internal structure cracks, a delay time should precede the setting time (on average, 30 min after mixing). Second, increases in moisture and temperature within the microwave cavity should be minimal. It is concluded that low-pressure microwave treatment substantially improves the properties of Portland cement pastes by increasing the resistance to drying shrinkage and water permeability.

Predicting the drying shrinkage behavior of high strength portland cement mortar under the combined influence of fine aggregate and steel micro fiber

The workability, 28-day compressive strength and free drying shrinkage of a very high strength (121-142 MPa) steel micro fiber reinforced portland cement mortar were studied under a combined influence of fine aggregate content and fiber content. The test results showed that an increase in the fine aggregate content resulted in decreases in the workability, 28-day compressive strength and drying shrinkage of mortar at a fixed fiber content. An increase in the fiber content resulted in decreases in the workability and drying shrinkage of mortar, but an increase in the 28-day compressive strength of mortar at a fixed fine aggregate content. The modified Gardner model most accurately predicted the drying shrinkage development of the high strength mortars, followed by the Ross model and the ACI 209R-92 model. The Gardner model gave the least accurate prediction for it was developed based on a database of normal strength concrete.

A Comparative Study Between the Early Stages Hydration of a High Strength and Sulphate Resistant Portland Cement and the Type II F Portland Cement Through Non Conventional Differential Thermal Analysis and Thermogravimetry

This work presents a study, which compares the early stages of hydration of a High Initial Strength and Sulphate Resistant Portland Cement (HIS SR PC) with those of Type II F Portland Cement (PC II), by Non-Conventional Differential Thermal Analysis (NCDTA) within the first 24 hours of hydration. Water/cement (w/c) ratios equal to 0.5, 0.6 and 0.66 were used to prepare the pastes. The hydration of these two types of cement was monitored on real time by NCDTA curves, through the thermal effects of the hydration reactions, from which cumulative evolved energy curves were obtained. These techniques allow one to analyse the influence of each type of cement on the main stages that occur during the hydration process. Thermogravimetric analysis were also performed at 4 and 24h of hydration for both cements, to analyse the influence of each kind of cement on the amount of the main formed hydrated products. The results showed that with 4h of hydration, the total combined water amount released from the hydrated products was higher for the PC II pastes than for the HIS SR PC pastes. Otherwise, with 24h of hydration, the amount of the total combined water released from the hydrated products was higher for the HIS SR PC pastes than for the PC II pastes.

Evaluation of Shrinkage Resulted Cracking of High Strength Calcium Sulfoaluminate Cement Concrete with Impact of Internal Curing

In this paper, restrained ring test and shrinkage test are carried on three kinds of concrete—high-strength portland cement concrete, high-strength calcium sulfoaluminate cement concrete and high-strength calcium sulfoaluminate cement concrete with internal curing in order to evaluate the shrinkage induced cracking performance of the concretes. The experimental results show that calcium sulfoaluminate cement concrete exhibits lower shrinkage caused by surface drying comparing to portland cement concrete. Internal curing can eliminate most of the autogenous shrinkage of concrete. In the ring test, the latter two concrete did not crack during the whole test history—42 days, while high-strength portland cement concrete cracked at the 13th day after casting. High strength calcium sulfoaluminate cement concrete exhibits better anti-cracking ability than the high strength portland cement concrete with the same strength grade.

Chemical activation of clay in cement mortar, using calcium chloride

Clay exhibits pozzolanic activity, if it is used in high-strength Portland cement. The pozzolonic reactivity of the clay can be enhanced by various methods. In this work the effect of clay on the strength of cement has been investigated in the presence and absence of CaCl2.2H2O as a chemical activator. It was found that the strength of cement mortar has been significantly increased by using an aqueous solution of calcium chloride instead of water. The addition of CaCl2.2H2O decreased the evaporable moisture and pH of the extract as compared to the hardened cement paste, which shows enhanced pozzolanic reactions between lime and clay. The optimum clay replacement level was found to be 10% without activator and 20% in the presence of 4% CaCl2.2H2O. The parameters such as the strength development and water extraction showed that CaCl2.2H2O was a good chemical activator for a clay-cementitious system.

Effect of aggregate size on spalling of geopolymer and Portland cement concretes subjected to elevated temperatures

This paper presents a study on the effect of aggregate size on spalling of concrete in fire. Three concretes with completely different chemical compositions and strengths were investigated, namely, geopolymer concrete and high strength and normal strength Portland cement concretes. The effect of aggregate size was found to be the same regardless of the type of concrete. The concretes containing 10mm aggregates spalled while the ones with 14mm did not spall. Since this effect is the same in geopolymer and Portland cement concretes, it is independent of binders’ chemical compositions. This paper shows that the degree of spalling has a good correlation to the fracture process zone length, which increases with increasing aggregate size; this in turn reduces the flux of kinetic energy from pore pressure and thermal stress that is released into the fracture front and thereby improves the spalling resistance.

Use of bagasse ash in cement and its impact on the mechanical behaviour and chloride resistivity of mortar

In this investigation bagasse ash from the sugar industries of Khyber Pakhtoon Khwa was utilised in high-strength Portland cement mortar. The effects of bagasse ash content on the physical and mechanical properties of hardened mortar were studied, which include compressive strength, consistency, setting time and chloride diffusion. The results indicated that bagasse ash was an effective mineral admixture and pozzolan. The optimum replacement ratio of bagasse ash was found to be 20% of the cement, which reduced the chloride diffusion effectively up to more than 50%, without any adverse effects on other properties of the hardened cement mortar.

Geopolymer and Portland cement concretes in simulated fire

High-strength Portland cement concrete has a high risk of spalling in fire. Geopolymer, an environmentally friendly alternative to Portland cement, is purported to possess superior fire-resistant properties. However, the spalling behaviour of geopolymer concrete in fire is unreported. In this paper, geopolymer and Portland cement concretes of strengths from 40 to 100 MPa were exposed to rapid temperature rises, simulating fire exposures. Two simulated fire tests, namely rapid surface temperature rise exposure test and standard curve fire test, were conducted. In both types of test, no spalling was found in geopolymer concretes, whereas the companion Portland cement concrete exhibited spalling. This can be attributed to different pore structures of the two concretes. The sorptivity test found that geopolymer concrete had a significantly higher sorption, therefore more connected pores, than Portland cement concrete when compared at the same strength level. Hence, it is suggested that the water vapour can escape from the geopolymer matrix quicker than in Portland cement concrete, resulting in lower internal pore pressure. The paper concludes that, when compared at the same strength level, the geopolymer concrete possesses higher spalling resistance in a fire than Portland cement concrete due to its increased porosity.

Use of clay as a pozzolona in high strength Portland cement and its thermal activation

In this investigation local clay from Cherat mines, Nowshera District, NWFP, Pakistan, has been tested as a pozzolanic material in high strength Portland cement. Thermal treatments were performed as a means of activation of the clay. It was found that thermal treatment of the clay can increase its pozzolanic activity. Different blended mortars, containing different amounts of clay, activated at different temperatures were studied for compressive strength, consistency, and setting times. It was concluded that the mechanical properties of the blended cements were mainly governed by the percentage of incorporation of the calcined clay. Blended cement composition has been formulated, with optimal results of 20% calcined clay at a temperature of 600°C.

Flow Behavior of Fresh Very High Strength Portland Cement Pastes

Flow behavior of fresh very high strength portland cement pastes prepared at various water/cement ratios was studied by using a rate-controlled coaxial cylinder viscometer (Rotovisko-Haake 20, system M5-osc., measuring device MV2P with serrated surfaces). The tests were performed under continuous flow conditions. Experimental shear stress and shear rate data were fitted very satisfactorily with various models, one of which has already been proposed by the authors. Excellent results were achieved also by applying the Quemada equation. In addition, the influence of two different commercial superplasticizing agents (Concretan RX and Ergomix 1000, the former based on polycyclic copolymers with modified structures, carrying hydroxylated side chains, and the latter on a modified polyacrylic resin) was studied with the aim of determining their optimum dosage and verifying the effectiveness by comparing rheological results with those obtained in a previous work on an ordinary portland cement. The use of superplasticizers modified rheological behavior of the pastes; however, no value of optimum dosage was found for any additive, but only a superplasticizer concentration range within which pastes presented very low values of viscosity. Moreover, both superplasticizers showed a greater effectiveness when added to HSPC pastes rather then the OPC ones formulated with the same water/cement ratio.

Rheological Properties of Very High-Strength Portland Cement Pastes: Influence of Very Effective Superplasticizers

The influence of the addition of very effective superplasticizers, that are commercially available, employed for maximising the solid loading of very high-strength Portland cement pastes, has been investigated. Cement pastes were prepared from deionized water and a commercially manufactured Portland cement (Ultracem 52.5 R). Cement and water were mixed with a vane stirrer according to ASTM Standard C305. The 0.38 to 0.44 water/cement ratio range was investigated. Three commercial superplasticizing agents produced by Ruredil S.p.a. were used. They are based on a melamine resin (Fluiment 33 M), on a modified lignosulphonate (Concretan 200 L), and on a modified polyacrylate (Ergomix 1000). Rheological tests were performed at 25°C by using the rate controlled coaxial cylinder viscometer Rotovisko-Haake 20, system M5-osc., measuring device MV2P with serrated surfaces. The tests were carried out under continuous flow conditions. The results of this study were compared with those obtained in a previous article for an ordinary Portland cement paste.

Raw mix designing, clinkerization and manufacturing of high-strength Portland cement from the limestone and clay of Darukhula Nizampur, Nowshera District, North-West Frontier Province (N.W.F.P.), Pakistan

This paper covers the detailed version of the potential raw material deposits at Darukhula and the adjacent areas of Nizampur, the manufacturing of high-strength Portland cement samples from the same material and comparison of the physical and chemical parameters for resulting cement with British and Pakistan standard specifications, which include compressive strength, setting time, consistency, lechatelier expansion, Blaine and insoluble residue. It was found that the raw material available in the study area meets the standard specifications and the area is feasible for the cement plant installation. The area can provide raw material which is quite sufficient for the running of a cement plant.

Chemical study of limestone and clay for cement manufacturing in Darukhula, Nizampur District, Nowshera, North West Frontier Province (N.W.F.P.), Pakistan

Limestone and clay samples were collected from Darukhula and adjoining areas of the Nizampur District, Nowshera, N.W.F.P., Pakistan, and analyzed for different parameters in order to search for new reserves of suitable material for the manufacture of different types of cements in N.W.F.P. It was found that the area under study contains three types of limestones, including high grade limestone, Darukhula limestone and siliceous limestone, which contain 53%, 49.03% and 45.19% CaO, respectively, and three types of clay, including maroon color, yellow to yellowish-green color and green color clay containing 57.76%, 65.47% and 61.24% SiO2, respectively. Chemical analysis of the limestone and clay samples collected from the deposits in the area under study showed that all the elements found in these samples are within the range of permissible limits for the production of high-strength Portland cement, sulphate resisting cement and white cement. This paper covers the detailed version of the potential raw material deposits at Darukhula and adjoining areas of the Nizampur District.

Investigations on the use of garnet granulites in the preparation of high strength portland cement

The preparation of ordinary portland cement (OPC), 43 grade as per I.S.: 8112 is possible by using garnet bearing granulites from the chalk hills of Salem, as a replacement material for argillaceous components in cement raw meal. The petrographic study of garnet granulites reveals the presence of minerals like garnet, clinopyroxene, plagioclase feldspar, chlorite, hornblende, biotite and quartz. In the present investigation the enhanced reactivity is noticed from 1250°C to 1350°C. The performance of the cement exhibits excellent strength properties with 310 Kg./cm 2, 420 Kg/cm 2, 460 Kg/cm 2 and 500 Kg/cm 2 for 1, 3, 7 and 28 days respectively. Presence of high alkalis in the cement slightly accelerated the setting time and raised the early strength. The paper describes briefly the geological background and various litho units present in the chalk hills. The field characteristics and petrography of garnet granulites are also described.