Strength development of ternary blended cement with limestone filler and blast-furnace slag

The benefits of limestone filler (LF) and granulated blast-furnace slag (BFS) as partial replacement of portland cement are well established. However, both supplementary materials have certain shortfalls. LF addition to portland cement causes an increase of hydration at early ages inducing a high early strength, but it can reduce the later strength due to the dilution effect. On the other hand, BFS contributes to hydration after seven days improving the strength at medium and later ages.Mortar prisms in which portland cement was replaced by up to 20% LF and 35% BFS were tested at 1, 3, 7, 28 and 90 days. Results show that the contribution of LF to hydration degree of portland cement at 1 and 3 days increases the early strength of blended cements containing about 5–15% LF and 0–20% BFS. The later hydration of BFS is very effective in producing ternary blended cements with similar or higher compressive strength than portland cement at 28 and 90 days. Additionally, a statistical analysis is presented for the optimal strength estimation considering different proportions of LF and BFS at a given age. The use of ternary blended cements (PC–LF–BFS) provides economic and environmental advantages by reducing portland cement production and CO₂ emission, whilst also improving the early and the later compressive strength.     

Compressive strength and chloride resistance of self-compacting concrete containing high level fly ash and silica fume

The influence of high-calcium fly ash and silica fume as a binary and ternary blended cement on compressive strength and chloride resistance of self-compacting concrete (SCC) were investigated in this study. High-calcium fly ash (40–70%) and silica fume (0–10%) were used to replace part of cement at 50, 60 and 70 wt.%. Compressive strength, density, volume of permeable pore space (voids) and water absorption of SCC were investigated. The total charge passed in coulombs was assessed in order to determine chloride resistance of SCC. The results show that binary blended cement with high level fly ash generally reduced the compressive strength of SCC at all test ages (3, 7, 28 and 90 days). However, ternary blended cement with fly ash and silica fume gained higher compressive strength after 7 days when compared to binary blended fly ash cement at the same replacement level. The compressive strength more than 60 MPa (high strength concrete) can be obtained when using high-calcium fly ash and silica fume as ternary blended cement. Fly ash decreased the charge passed of SCC and tends to decrease with increasing fly ash content, although the volume of permeable pore space (voids) and water absorption of SCC were increased. In addition when compared to binary blended cement at the same replacement level, the charge passed of SCC that containing ternary blended cement was lower than binary blended cement with fly ash only. This indicated that fly ash and silica fume can improve chloride resistance of SCC at high volume content of Portland cement replacement.     

Optimization of calcium chloride content on bioactivity and mechanical properties of white Portland cement

This research investigates the optimization of calcium chloride content on the bioactivity and mechanical properties of white Portland cement. Calcium chloride was used as an addition of White Portland cement at 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10% by weight. Calcium chloride was dissolved in sterile distilled water and blended with White Portland cement using a water to cement ratio of 0.5. Analysis of the bioactivity and pH of white Portland cement pastes with calcium chloride added at various amounts was carried out in simulated body fluid. Setting time, density, compressive strength and volume of permeable voids were also investigated. The characteristics of cement pastes were examined by X-ray diffractometer and scanning electron microscope linked to an energy-dispersive X-ray analyzer. The result indicated that the addition of calcium chloride could accelerate the hydration of white Portland cement, resulting in a decrease in setting time and an increase in early strength of the pastes. The compressive strength of all cement pastes with added calcium chloride was higher than that of the pure cement paste, and the addition of calcium chloride at 8 wt.% led to achieving the highest strength. Furthermore, white Portland cement pastes both with and without calcium chloride showed well-established bioactivity with respect to the formation of a hydroxyapatite layer on the material within 7 days following immersion in simulated body fluid; white Portland cement paste with added 3%CaCl₂ exhibited the best bioactivity.     

Behaviour of ASTM Type V cement hydrated in the presence of sulfonated melamine formaldehyde

ASTM Types I and V Portland cements were hydrated up to 28 days in the presence of 0.3% and 0.6% sulfonated melamine formaldehyde (SMF), at a water/cement ratio of 0.35. Hydration was studied by conduction calorimetric and thermogravimetric analyses. The amount of Ca(OH)₂ produced, compressive strength and porosity were determined after 1, 3, 7 and 28 days of curing. The compressive strengths of all samples increased with the age of curing. In the period studied the values decreased in the order: Type I cement (reference)=Type I cement+SMF>Type V cement (reference)≥Type V cement+SMF. The superplasticizer addition retarded the development of heat in the cements, but more severely in Type V cements. Porosities were generally higher for samples with lower compressive strengths. In the presence of 0.6% SMF, the early low strengths in Type V cement mixtures could be attributed to lower degrees of hydration. At later ages, the microstructure rather than the degree of hydration determined the strength development. However, incorporation of 0.3% SMF in Type V cement did not affect its strength development.     

Influence of 15 and 80 nano-SiO2 particles addition on mechanical and physical properties of ternary blended concrete incorporating rice husk ash

This study demonstrates the effects of SiO₂ nanoparticles as additives with two different sizes of 15 and 80?nm on compressive strength and porosity of rice husk ash (RHA) blended concrete. Up to 20% of ordinary Portland cement (OPC) was replaced by RHA with average particle size of 5 micron. Also, SiO₂ nanoparticles were added to the above mixture at four different weight percentages of 0.5, 1.0, 1.5 and 2.0 and cured in lime solution. The results indicated that compressive strength of Portland cement–nano SiO₂–rice husk ash (PC–NS–RHA) ternary blended concrete was considerably increased. Moreover, the total amount of porosity decreased to a minimum with respect to the control concrete. This improvement was observed at all the curing ages and replacement levels, but there was a gain in the optimal point with 20% of RHA plus 2% of 80?nm SiO₂ particles at 90 days of curing.     

Chemical activation of hybrid binders based on siliceous fly ash and Portland cement

The hydration of Portland cement (PC) blended with a high amount of a siliceous fly ash (70% fly ash, 30% PC) has been examined. The fly ash contributes significantly to the long-term strength development, when compared to a reference sample with quartz powder. However the long setting time and the poor early strength prevent the use of such binders. Therefore the effect of different activators (sodium carbonate, potassium sodium silicate, potassium citrate and sodium oxalate) on the setting, the hydration kinetics and the strength development of the fly ash-PC blend has been investigated.The addition of the activators increases the pH and decreases thus the calcium concentrations in the pore solution, which leads to a faster reaction of alite and thus to early setting and increased early strength. On the long term, the high alkali concentrations lower the compressive strength and lead to a (partial) destabilization of ettringite.Sodium oxalate and potassium sodium silicate accelerate both the setting of the fly ash-PC blend and increase the early compressive strength. Furthermore, they show better compressive strengths at later ages compared to the other activators. Based on these findings, they can be considered as the most suitable accelerators among the investigated activators.     

Compressive strength and drying shrinkage of fly ash-bottom ash-silica fume multi-blended cement mortars

This paper studies the physical properties, compressive strength and drying shrinkage of multi-blended cement under different curing methods. Fly ash, ground bottom ash and undensified silica fume were used to replace part of cement up to 50% by weight. Specimens were cured in air at ambient temperature, water at 25, 40 and 60 °C, sealed with plastic sheeting for 28 days. The results show that absorption and volume of permeable pore space (voids) of blended cement mortars at 28 day under all curing methods tend to increase with increasing silica fume replacement. The compressive strength of blended cement with fly ash and bottom ash was lower than that of Portland cement control at all curing condition while blended cement with silica fume shows higher compressive strength. In addition, the compressive strength of specimens cured with water increased with increasing curing temperature. The drying shrinkage of all blended cement mortar cured in air was lower than that of Portland cement control while the drying shrinkage of blended cement mortar containing silica fume, cured with plastic sealed and water at 25 °C was higher than Portland cement control due to pore refinement and high autogenous shrinkage. However, the drying shrinkage of blended cement mortar containing SF cured with water at 60 °C was lower than that of Portland cement control due to lower autogenous shrinkage and the reduced microporosity of C–S–H.     

Micro-structural development of gap-graded blended cement pastes containing a high amount of supplementary cementitious materials

To clarify the strength improvement mechanism of gap-graded blended cements with a high amount of supplementary cementitious materials, phase composition of hardened gap-graded blended cement pastes was quantified, and compared with those of Portland cement paste and reference blended cement (prepared by co-grinding) paste. The results show that the gap-graded blended cement pastes containing only 25% cement clinker by mass have comparable amount of gel products and porosity with Portland cement paste at all tested ages. For gap-graded blended cement pastes, about 40% of the total gel products can be attributed to the hydration of fine blast furnace slag, and the main un-hydrated component is coarse fly ash, corresponding to un-hydrated cement clinker in Portland cement paste. Further, pore size refinement is much more pronounced in gap-graded blended cement pastes, attributing to high initial packing density of cement paste (grain size refinement) and significant hydration of BFS.     

High-volume natural volcanic pozzolan and limestone powder as partial replacements for portland cement in self-compacting and sustainable concrete

A laboratory study demonstrates that high volume, 45% by mass replacement of portland cement (OPC) with 30% finely-ground basaltic ash from Saudi Arabia (NP) and 15% limestone powder (LS) produces concrete with good workability, high 28-day compressive strength (39 MPa), excellent one year strength (57 MPa), and very high resistance to chloride penetration. Conventional OPC is produced by intergrinding 95% portland clinker and 5% gypsum, and its clinker factor (CF) thus equals 0.95. With 30% NP and 15% LS portland clinker replacement, the CF of the blended ternary PC equals 0.52 so that 48% CO₂ emissions could be avoided, while enhancing strength development and durability in the resulting self-compacting concrete (SCC). Petrographic and scanning electron microscopy (SEM) investigations of the crushed NP and finely-ground NP in the concretes provide new insights into the heterogeneous fine-scale cementitious hydration products associated with basaltic ash-portland cement reactions.     

The effect of temperature on the hydration of composite cements containing limestone powder and fly ash

The effect of the curing temperature (5, 20 and 40°C) on the degree of hydration, amount of bound water and calcium hydroxide, porosity and the development of mechanical properties was investigated on pastes and mortars prepared with fly ash (FA)?Climestone (L) Portland composite cements. Increasing the curing temperature for ordinary Portland cement (OPC) leads to a more inhomogeneous distribution of hydration products, resulting in an increased coarse porosity and therefore a lower compressive strength after 7?days and longer. In contrast, the FA containing mortars showed higher compressive strength with increasing curing temperature up to 90?days. The reaction of the FA is increased at 40°C and strongly retarded at 5°C. At 20 and 40°C, FA reduces the porosity at later ages. The replacement of 5% of the OPC or FA by L powder did not impair the strength at 5 and 20°C, but lowered strength slightly at 40°C for the FA blended cements. The porosity appears to be the dominating factor regarding the compressive strength, independent of whether part of the OPC is replaced by FA and L powder or not.     

Characterization and properties of portland cement composites incorporating zinc-iron oxide nanoparticles

The present work exposes preliminary results concerning ordinary Portland cement (OPC) blended with oxide fumes produced in steel smelting plants and known as electric arc furnace dust (EAFD). After acid treatment of the EAFD, the powder obtained was formed basically of nanometric particles of ZnFe₂O₄. The incorporation of EAFD to OPC produced a small retardation of the setting process. Nevertheless, after 7 days the compressive strength of the OPC/EAFD pastes was superior and after 28 days the extent of hydration in OPC and OPC/EAFD pastes was equivalent. The present results indicate that a compressive strength of 72 MPa can be attained after 42 days for OPC doped with 10 wt% of EAFD.     

Mathematical model for the prediction of cement compressive strength at the ages of 7 and 28 days within 24 hours

In this study 450 cement mortar cubes were cast from 50 different cement samples taken from 9 different cement factories, to develop a mathematical model that can predict Portland cement compressive strength at ages 7 and 28 days within 24 hours only. This is in order to save time and expense, that is lost in waiting for such a long period, and for quality control assurance for both produced cement (in cement factories), and concrete mixes in constructions. In addition, attention has been made on the right choice of variables of the cement itself (phase composition and fineness). In addition, an attempt has been made to use other variables that are believed to affect compressive strength of Portland cement as the minor oxides MgO, SO₃ and soundness. Other variables obtained from chemical analysis of the cement as LOI, IR, and LSF were also included in the model. The most important thing in this study is to get use of the concept of using early age strength to predict Portland cement strength at later ages for the first time. An attempt was made to combine both accelerated strength testing (as an early strength and UPV of cement mortar specimens), with the characteristics of the cement mentioned above, in predicting the compressive strength of cement. It was found that the accelerated strength yields good and high correlation with the compressive strength of cement, especially at the age of 28 days. In this work too, the importance of the ultrasonic pulse velocity (UPV) and mortar density were evident and the usefulness of using these variables in predicting the compressive strength of the cement was proved (because of fixing most of the factors affecting this property). Thus, it is possible to have good results that can be used in the prediction of compressive strength of cement. It was found that using each of the accelerated compressive strength f_acc, UPV and density of the mortar cubes yielded high correlation with the compressive strength than any of the other variables. Different combinations of variables were introduced into the model, in order to choose the variables that can significantly predict the cement compressive strength. In this work, it was possible to obtain a model that can predict the cement strength with standard errors of only 1.887 and 1.904 MPa and coefficients of correlation of 0.903 and 0.928, for cement strengths at 7 and 28 days respectively.     

Influence of activated fly ash on corrosion-resistance and strength of concrete

Various activation techniques, such as physical, thermal and chemical were adopted. By adopting these methods of activation, hydration of fly ash blended cement was accelerated and thereby improved the corrosion-resistance and strength of concrete. Concrete specimens prepared with 10%, 20%, 30% and 40% of activated fly ash replacement levels were evaluated for their compressive strengths at 7, 14, 28 and 90 days and the results were compared with ordinary Portland cement concrete (without fly ash). Corrosion-resistance of fly ash cement concrete was studied by using anodic polarization technique. Electrical resistivity and ultrasonic pulse velocity measurements were also carried out to understand the quality of concrete. The final evaluation was done by qualitative and quantitative estimation of corrosion for different systems. All the studies confirmed that upto a critical level of 20–30% replacement; activated fly ash cement improved both the corrosion-resistance and strength of concrete. Chemical activation of fly ash yielded better results than the other methods of activation investigated in this study.     

Influence of pozzolana on sulfate attack of cement stone affected by chloride ions

This study investigated the influence of natural pozzolana (opoka) additive on the hydration of Portland cement and the effects of pozzolana on sulfate attack of cement stone affected by chloride ions. In the samples, 25 % (by weight) of the Portland cement was replaced with pozzolana. The specimens were hardened for 28 days in water, and then one batch was soaked in a saturated NaCl solution and another in a 5 % Na₂SO₄ solution for 3 months at 20 °C. After being kept for 3 months in a saturated NaCl solution, samples were transferred to a 5 % Na₂SO₄ solution and kept under these conditions for 3 months. It was estimated that under normal conditions, pozzolana additive accelerated the hydration of calcium silicates and initiated the formation of CO₃ ^2?–AFm; opoka also decreased the threshold pore diameter of hardened Portland cement paste. It was found that Cl^– ions penetrate to monosulfoaluminate, form Friedel’s salt, and release SO₄ ^2? ions, which react with unaffected monosulfoaluminate and form extra ettringite; when samples were transferred to the 5 % Na₂SO₄ solution, a greater quantity of new ettringite was formed. Meanwhile, pozzolana additive reduced the penetration of chloride and sulfate ions into the structure of Portland cement hydrates and inhibited sulfate attack of cement stone treated in a saturated NaCl solution.     

Combined effect of chemical nature and fineness of mineral powders on Portland cement hydration

This paper focuses on the influence of the chemical nature and the fineness of the fillers on the hydration process and on the compressive strength development. Four different types of fillers are considered in combination with Portland cement: quartzite filler, alumina filler, limestone filler, and silica fume. The study deals with blended mortars having a 0.45 water to powder (cement and filler) ratio with a 10% substitution of cement by filler. Quartzite fillers do not seem to accelerate the hydration process in a significant way. No positive effect is noticed on the strength development either. The presence of a fine inert alumina powder increases the rate of early hydration of Portland cement. The greater the fineness, the faster the rate of hydration heat development. This reactivity leads to an increase in the compressive strength at early age for mortar containing the finest alumina powders. In case of coarse alumina powder, no acceleration effect is obtained. Finely ground limestone (calcite) fillers promote heterogeneous nucleation of hydrates which significantly accelerates hydration. At early age, this also results in an increased mortar compressive strength in comparison with the control mortar. From the obtained results, it is clear that both chemical natures as well as fineness are important with regard to the accelerating effect of the hydration process. With increasing fineness, the accelerating effect increases. For powders with comparable fineness, it is clear that limestone powder has a more significant accelerating effect than silica fume and alumina filler. Quartzite filler seems to have no significant effect.     

Mineral wool production waste as an additive for Portland cement

This study aims at investigating the possibility of using dust, collected in air filters during the melting of mineral wool raw materials (mineral wool cupola dust) as an additive for Portland cement. It was found that the investigated dust mainly consists of quartz, periclase, albite, dolomite, and the amorphous phase. The main impurities are halite and sylvite. The investigated additive was additionally milled and prepared as a microfiller. The results showed that the cupola dust additive increases the initial hydration of cement, yet prolongs the dormant period. It was estimated that up to 15 wt% of Portland cement can be replaced by the dust additive without impairing the strength properties of samples after 28 days of hardening. However, after 90 days of hydration, the compressive strength of all samples with the investigated additive is lower than in pure OPC samples. This phenomenon is concerned with the formation of a significant amount of Friedel's salt. The content of chlorides in the raw material was reduced from 4.901 to 0.612 wt% by washing with water, when the water-to-solid ratio was equal to 10. The results of the investigation showed that the washed and ground cupola dust had a positive effect on the compressive strength of the cement samples. When 5, 10, and 15 wt% of prepared dust additive were used, the compressive strength of samples after 28 and 90 days of hydration was greater than that of pure Portland cement sample. The findings suggest that the additionally prepared dust additive leads to the formation of a stable structure of the cement stone, accelerates the calcium silicates hydration, and promotes the formation of gismondine.     

Influence of limestone and anhydrite on the hydration of Portland cements

The addition of CaCO₃ and CaSO₄ to Portland cement clinker influences the hydration and the strength development. An increase of the CaSO₄ content accelerates alite reaction during the first days and results in the formation of more ettringite, thus in a higher early compressive strength. The late compressive strength is decreased in Portland cements containing higher quantities of CaSO₄. The reduced late compressive strength seems to be related to an increase of the S/Si and Ca/Si content in the C–S–H.The presence of calcite leads to the formation of hemicarbonate and monocarbonate thus indirectly to more ettringite. Only a relatively small quantity of calcite reacts to form monocarbonate or hemicarbonate in Portland cement. Although hemicarbonate is thermodynamically less stable than monocarbonate, hemicarbonate formation is kinetically favored. Monocarbonate is present only after 1 week and longer independent of the quantity of calcite available and the content of sulphate in the cement.     

Effect of cement type and limestone particle size on the durability of steam cured self-consolidating concrete

This paper describes a laboratory program to investigate the influence of cement and limestone filler (LF) particle size on the hardened properties and durability performance of steam cured self-consolidating concrete. In addition, the interplay between cement type and LF particle size was investigated. CSA (Canadian Standards Association) Type GU (General Use) and HE (High Early-strength) cements were used with 5% silica fume (SF) [1]. The water-to-cement ratio was 0.34. LF with two nominal particle sizes of 17 μm and 3 μm, which correspond to Blaine fineness of 475 and 1125 m²/kg, respectively, were used. In addition to fresh concrete properties, hardened properties including compressive strength, elastic modulus, ultrasonic pulse velocity and density were measured at 12 h and 16 h, and at 3, 7 and 28 days. Indicators of durability performance including rapid chloride permeability testing (RCPT), sulfate resistance, linear shrinkage, salt scaling resistance and freeze-thaw resistance were evaluated. The results showed that LF improved the 12 and 16-h strength with no influence on later age strength (i.e., 3–28 days). The linear shrinkage and RCPT decreased with the addition of LF. This reduction was linked to the production of calcium mono-carboaluminate. LF did not impact the sulfate resistance, salt scaling resistance or freeze-thaw resistance of concrete.     

Evaluation of compressive strength of hardening silica fume blended concrete

Silica fume (SF) is a byproduct of induction arc furnaces and has long been used as a mineral admixture to produce high-strength and high-performance concrete. Owing to the pozzolanic reaction between calcium hydroxide and SF, compared with Portland cement, the hydration of concrete containing SF is much more complex. In this paper, by considering the production of calcium hydroxide in cement hydration and its consumption in the pozzolanic reaction, a numerical model is proposed to simulate the hydration of concrete containing SF. The degree of hydration of cement and degree of reaction of SF are obtained as accompanied results from the proposed hydration model. Furthermore, on the basis of the volume stoichiometries, mixing proportions and the degree of reactions of cement and SF, the gel–space ratio of hydrating blended concrete is calculated. Finally, the development of compressive strength of SF blended concrete is evaluated through Powers’ strength theory considering the contributions of cement hydration and SF reaction. The proposed model is verified through experimental data on concrete with different water-to-cement ratios and SF substitution ratios.     

Blended cements containing high volume of natural zeolites: Properties, hydration and paste microstructure

In this study, properties and hydration characteristics as well as paste microstructure of blended cements containing 55% by weight zeolitic tuff composed mainly of clinoptilolite mineral were investigated. Free Ca(OH)₂ content, crystalline hydration products and decomposition of zeolite crystal structure, pore size distribution and microstructural architecture of hydrated cement pastes were examined. Superplasticizer requirement and compressive strength development of blended cement mortars were also determined. The blended cements containing high volume of natural zeolites were characterized with the following properties; (i) no free Ca(OH)₂ in hardened pastes at the end of 28 days of hydration, (ii) less proportion of the pores larger than 50 nm when compared to portland cement paste, (iii) complete decomposition of crystal structure of zeolite at the end of 28 days of hydration, (iv) presence of tetra calcium aluminate hydrate as a crystalline product of pozzolanic reaction, (v) more compatibility with the melamine-based superplasticizer when compared to the naphthalene based product, and (vi) similar 28 days compressive strength of mortars to that of reference portland cement.