Sulfate resistance of plain and blended cement

This paper presents a laboratory study on the sulfate resistance of blended cement combination of reference Portland cement with high volume ground granulated blast-furnace slag (GGBS) and natural pozzolan (NP). The exposure solutions were tap water containing 5% magnesium sulfate solution and 5% sodium sulfate solution. Two types of grinding method (separately grinding and intergrinding, two finenesses (250 m²/kg and 500 m²/kg) and three different proportions (10%, 20%, and 30% by weight of mixture)) of each of two different additives (GGBS and NP) in equal amounts were employed. In addition to these blends, plain Portland cements without additives were prepared as references specimens. Standard Rilem sample size (40 mm × 40 mm × 160 mm) was used for the experimental study.It was observed that the sulfate resistances of blended cements were significantly higher both against sodium sulfate and magnesium sulfate attacks than references cement. Final strength reductions for finer mixes attacked by magnesium sulfate were marginally lower than those attacked by sodium sulfate. On the other hand, no particular relation was found between the sulfate resistance of the mortars and the grinding methods.     

Use of calcium carbide residue and bagasse ash mixtures as a new cementitious material in concrete

Calcium carbide residue (CCR) is a by-product of the acetylene gas production and bagasse ash (BA) is a by-product obtained from the burning of bagasse for electricity generation in the sugar industry. The mixture between CCR contains a high proportion of calcium hydroxide, while BA is a pozzolanic material, can produce a pozzolanic reaction, resulting in the products similar to those obtained from the cement hydration process. Thus, it is possible to use a mixture of CCR and BA as a cementitious material to substitute for Portland cement in concrete. The results indicated that concrete made with CCR and BA mixtures and containing 90 kg/m³ of Portland cement gave the compressive strength of 32.7 MPa at 28 days. These results suggested that the use of ground CCR and ground BA mixtures as a binder could reduce Portland cement consumption by up to 70% compared to conventional concrete that requires 300 kg/m³ of Portland cement to achieve the same compressive strength. In addition, the mechanical properties of the alternative concrete including compressive strength, splitting tensile strength, and elastic modulus were similar to that of conventional concrete.     

Influence of activated drinking-water treatment waste on binary cement-based composite behavior: Characterization and properties

Drinking water treatment plants regularly dispose of large volumes of industrial sludge in landfill sites, which often has negative environmental consequences. The calcination products of these kaolinite-based sludges have properties that could make them appropriate supplementary cementing materials in the production of blended binary cements.This research analyses the pozzolanic and thermodynamic properties of a Venezuelan drinking water sludge activated at 600 °C for 2 h and its behavior in blended cement matrices prepared with 15% Activated Waste (AW) and 85% Ordinary Portland Cement (OPC). Our results show that this activated drinking water sludge presents high pozzolanic properties, mainly during the first 24 h of reaction. The XRD, SEM/EDX and thermodynamic studies confirm the formation of C₂ASH₈, C–S–H gels and C₄AH₁₃ as the hydration products from the pozzolanic reaction. The binary mixture of 15% AW/85% OPC complied with the physical and mechanical specifications contained in current European cement standards.     

Glass waste as supplementary cementing materials: The effects of glass chemical composition

Sustainable cements containing 25 wt% of different types of recycled glass have been investigated as a supplementary cementing material in order to highlight the role of glass chemical composition during the hardening process. Glass formers, stabilizers and modifiers regulate the glass dissolution in the alkaline environment during cement hydration. As a consequence, pozzolanic reaction and/or alkali–silica reaction are strictly related to the glass chemical composition. The mechanical and microstructure characterizations of mortar samples containing glass blended cements and un-reactive aggregates allow to determine which oxides in the glass have to be carefully monitored to avoid deleterious reactions.     

Characterization and properties of blended cement matrices containing activated bamboo leaf wastes

The worldwide production of bamboo generates large volumes of leaf wastes, which are deposited in landfills or burned in an uncontrolled manner, with negative effects in the environment. The ash obtained by calcining of the bamboo leaf waste, shows good qualities as supplementary cementing material for the production of blended cements.The current paper shows a detailed scientific study of a Brazilian bamboo leaf ash (BLA) calcined at 600 °C in small scale condition, by using different techniques (XRF, XRD, SEM/EDX, FT–IR, TG/DTG) and technical study in order to analyse the behaviour of this ash in blended cements elaborated with 10% and 20% by mass of BLA. The results stated that this ash shows a very high pozzolanic activity, with a reaction rate constant K of the order of 10^?1/h and type I CSH gel was the main hydrated phase obtained from pozzolanic reaction. The BLA blended cements (10% and 20%) complied with the physical and mechanical requirements of the existing European standards.     

Characterisation of ground hydrated Portland cement-based mortar as an additive to alkali-activated slag cement

The sustainable development of cement manufacturing requires extension of the raw material base, including large-tonnage waste. Hydrated mortar waste is a promising mineral resource for the production of Portland cements and alternative binders, such as alkali-activated slag cement. The influences of ground-hydrated mortar aged for 3 months on the properties of alkali-activated slag fresh and hardened pastes were performed. The results show that the properties are dependent on the concentration (2.5–60%), cement:sand ratio (1:1–3) and fineness (200–600 m²/kg) of the ground hydrated mortar; the alkali activator (sodium carbonate and sodium silicate); and the curing conditions (normal conditions and steam curing). The fresh paste properties that we considered in this study included the water requirement and the setting time; the hardened paste properties we considered were the water absorption, the density, and the compressive strength after 2, 7, 14, 28, 180 and 360 days of ageing. The ground hydrated mortar improved the early strength and the long-term strength of the alkali-activated slag paste and replaced the slag up to 50%. The factors that affecting the strength of the alkali-activated slag cement with ground hydrated mortar as an additive were, in order of influence, alkali activator type > curing conditions > cement:sand ratio > ground-hydrated mortar fineness.     

Statistical analysis for freeze–thaw resistance of cement mortars containing marble dust and glass fiber

This paper investigated the usability of marble dust and glass fiber against the harmful effects of freeze–thaw (FT) cycles on cement mortars as experimentally and statistically. To this end, the cement mortar specimens containing marble dust (0%, 20%, 40% and 50% by volume) and glass fiber (0 kg/m³, 0.25 kg/m³, 0.50 kg/m³, 0.75 kg/m³) were prepared. The compressive and flexural strengths of the specimens were determined after being exposed to FT cycles. In order to reduce the numbers of experiments, an L₁₆ (4² × 2¹) Taguchi orthogonal array was adopted to the study. Amounts of glass fiber, percentages of marble dust and cycles of freeze–thaw, were changed to explore their effects on the compressive and flexural strengths of the mortar specimens. Statistically effects of the factors were also determined by using analysis of variance (ANOVA) method. Finally, experimental findings were compared with statistical results and a good agreement between them was achieved.     

The role of RHA-blended cement in stabilizing metal-containing wastes

Time to final setting, strength development and leachability of heavy metals from the solidified wastes using reactive rice husk ash (rRHA)-blended cement as solidification binder were investigated. The rRHA was prepared by firing at 650 °C for 1 h. Synthetic metal hydroxides and plating sludge were solidified using cement blended with 0, 10, 20 and 30 wt.% rRHA. Experimental results showed that synthetic Zn(OH)₂ and the plating sludge caused rapid setting for cement paste but prolong the final setting for rRHA-blended cements. The rate of strength development was also decreased during the first 14 days of curing. However, these interfering effects were reduced when cement was blended with 10 wt.% rRHA. In addition, the plating sludge could be loaded at 30 wt.% to the cement blended with 10 wt.% rRHA and gave both the 28-day strength and metal concentration in TCLP leachates that meet the regulatory limits for landfilling.     

Effect of curing temperature on the nonevaporable water in portland cement blended with geothermal silica waste

This paper reports the results of the utilization of a silica waste from a geothermal power generation plant as partial replacement of portland cement. To evaluate the reactivity of the silica waste, the effect of the curing temperature was analyzed by means of the estimation of nonevaporable water (NEW) and calcium hydroxide (CH) contents. Pastes of portland cement substituted with 0%, 5%, 10% and 15% of geothermal silica waste (GSW) and water/solid ratio of 0.50 were cured at 10, 20, 40 and 60 °C for up to 540 days. The pastes were characterized by thermogravimetric analysis. According with the CH estimations, the geothermal silica showed a strong pozzolanic behavior. Nevertheless, the NEW contents were lower compared to those of neat cement, in agreement with other reports. The results of NEW contents of neat and blended cements were processed to obtain a modified NEW (mNEW) that excluded the water corresponding to the CH. The mNEW data indicated that the blended cements reached higher contents of nonevaporable water.     

A study on reinforcement corrosion and related properties of plain and blended cement concretes under different curing conditions

This paper presents the results of an experimental investigation on the steel reinforcement corrosion, electrical resistivity, and compressive strength of concretes. Concretes having two different water–cement ratios (0.65 and 0.45) and two different cement contents (300 and 400 kg/m³) were produced by using a plain and four different blended portland cements. Concrete specimens were subjected to three different curing procedures (uncontrolled, controlled, and wet curing). The effect of using plain or blended cements on the resistance of concrete against damage caused by corrosion of the embedded reinforcement has been investigated using an accelerated impressed voltage setup. The resistivity of the cover concrete has been measured non-destructively by placing electrodes on concrete surface. The compressive strength, electrical resistivity, and corrosion resistance of the concretes were determined at different ages up to 180 days. The results of the tests indicated that the wet curing was essential to achieve higher strength and durability characteristics for both plain and especially blended cement concretes. The concretes, which received inadequate (uncontrolled) curing, exhibited poor performance in terms of strength and corrosion resistance.     

Durability of mixtures containing calcium nitrite based corrosion inhibitor

The influence of calcium nitrite based corrosion inhibitor on the corrosion of reinforcing steel embedded in 14 different mortars is experimentally investigated in this work. Two Portland cements, NPC and SR (type I and V according to ASTM Standards) and 12 blended cements were used. The pozzolanic materials used were three lignite fly ashes, silica fume and one natural pozzolan (Milos' Earth). All blended cements were produced in the laboratory by grinding Portland clinker, gypsum and the appropriate pozzolanic material. One commercially available blended cement (CEM II/A-M 32.5N) was also used in this research. Mortar specimens (cylinders 100 × 40 mm) were prepared, according to DIN 1164 with and without calcium nitrite and used for measurements of carbonation and chloride-induced corrosion for a time period of 2 years. Chloride resistance was monitored according to ASTM C876 on specimens immersed in a 5% NaCl solution after an initial curing of 28 days. The carbonation depth was measured on cylinders cured in a severe environment using a spray indicator enabling the estimation of different pH values.Results show that calcium nitrite has a beneficial effect in shifting the corrosion potential towards electropositive direction especially in the case of NPC and SR cements. The corrosion potential of blended mixtures was also shifted towards electropositive direction, but since the pozzolanic materials had a beneficial effect by themselves, the reduction was comparative smaller. The beneficial effect of calcium nitrite was also confirmed by the gravimetric weight loss measurements performed after 2 years of immersion in the 5% NaCl solution.Carbonation depth of all mixtures was reduced or remained the same when calcium nitrite was used. Chloride permeability was not seriously influenced by the addition of calcium nitrite, as it is indicated by the total chloride measurements performed after 2 years of immersion in the 5% NaCl solution.     

Scaling resistance of high performance concretes containing a small portion of pre-wetted lightweight fine aggregate

The subject of the investigation was the influence of pre-wetted lightweight aggregate on damage of the concrete surface due to cyclic freezing and thawing in the presence of de-icing salts tested according to the Swedish Standard SS 13 72 44 (the Borås method). Six series of concrete specimens were made with the same water/binder (w/b) ratio 0.32, cement volume 400 kg/m³ and content of superplasticiser 8.8 kg/m³. One series, S3/2, contained an air-entraining agent. Series S4/7 and S4/8 were made with water/cement ratio equal to 0.45 and a lower cement content 340 kg/m³. In a few series the sand fraction 0–2 mm and basalt fraction 2–4 mm were partly or totally replaced by wetted lightweight aggregate. Concretes S3/1, S3/3, S4/7 and S4/8, failed the test. The best results were obtained for concrete S3/6 (with the 2–4 mm fraction replaced by half) and S3/2 (air-entrained). The application of an air-entraining agent is more expensive than LWA, and at a construction site it is not always easy to control. It seems that the replacement of a part of aggregate by LWA could be a more effective way to improve the scaling resistance.     

Effect of activated coal mining wastes on the properties of blended cement

The large volumes of coal waste generated world-wide in mining operations are mostly deposited in refuse dumps, to the severe detriment of the surrounding groundwater and soil. After calcination under controlled conditions, this waste has been shown to exhibit high pozzolanicity, making it apt for use as an addition in the manufacture of blended cements.The present paper describes the first detailed study designed to evaluate the behavior of coal tailings from different sources. After activation at 650 °C for 2 h, this waste was used to manufacture blended cements containing 10 and 20 wt.% of the addition. Inclusion of this pozzolan did not affect the initial setting time, although the compressive strength of the blended mortars declined, by 4.7–8.3% in the 10% and by 9.76–14.9% in the 20% material. Nonetheless, the activated carbon waste (ACW) blends complied with all the requirements for Type II/A cement in the existing European legislation.     

Measuring the eco-efficiency of cement use

At present, the cement industry generates approximately 5% of the world’s anthropogenic CO₂ emissions. This share is expected to increase since demand for cement based products is forecast to multiply by a factor of 2.5 within the next 40 years and the traditional strategies to mitigate emissions, focused on the production of cement, will not be capable of compensating such growth. Therefore, additional mitigation strategies are needed, including an increase in the efficiency of cement use. This paper proposes indicators for measuring cement use efficiency, presents a benchmark based on literature data and discusses potential gains in efficiency. The binder intensity (bi) index measures the amount of binder (kg m^?3) necessary to deliver 1 MPa of mechanical strength, and consequently express the efficiency of using binder materials. The CO₂ intensity index (ci) allows estimating the global warming potential of concrete formulations. Research benchmarks show that bi ～5 kg m^?3 MPa^?1 are feasible and have already been achieved for concretes >50 MPa. However, concretes with lower compressive strengths have binder intensities varying between 10 and 20 kg m^?3 MPa^?1. These values can be a result of the minimum cement content established in many standards and reveal a significant potential for performance gains. In addition, combinations of low bi and ci are shown to be feasible.     

Lightweight screed containing cork granules: Mechanical and hygrothermal characterization

This paper presents the results of an experimental study on the use of expanded cork granule waste with cement-based mixtures to produce lightweight screeds as an overlay of a structural concrete slab. Lightweight screeds (LWSs) were made with Portland cement, sand, expanded cork granules (ECG) and water. These cork particles are industrial waste and are still a completely natural material even after industrial processing. The experiments were carried out on 3 cement dosages of 150 kg/m³, 250 kg/m³ and 400 kg/m³, incorporating expanded cork granules as replacement of part of the sand. Three additional mixtures without cork were prepared and used as reference. They had the same cement content as the lightweight ones. Hardened density, compressive strength, thermal conductivity, water vapor permeability, adsorption isotherms and water absorption by partial immersion of the mixtures were determined. Results show that the addition of expanded cork granules affects the screeds by decreasing their density, compressive strength and thermal conductivity while increasing their water vapor permeability.     

Influence of cement composition on the early age flexural strength of heat-treated mortar prisms

Heat treatment is extensively used to accelerate the process of the strength development of concrete for prefabrication purposes. This study was conducted to determine the effect of cement composition on the improvement of the one-day flexural strength of heat-treated mortar prisms. Considering the strength gain at the end of one day of heat treatment application, it can be concluded that a treatment temperature of 80 °C seems to be appropriate for CÇ 32.5 cement while it is 65 °C for the other cements tested. It is also concluded that an initial curing of 4 h is suitable in view of the technical success of heat treatment application. However, it may be shorter for blended cements for economic reasons.     

An experimental study on optimum usage of GGBS for the compressive strength of concrete

This paper presents a laboratory investigation on optimum level of ground granulated blast-furnace slag (GGBS) on the compressive strength of concrete. GGBS was added according to the partial replacement method in all mixtures. A total of 32 mixtures were prepared in four groups according to their binder content. Eight mixes were prepared as control mixtures with 175, 210, 245 and 280 kg/m³ cement content in order to calculate the Bolomey and Féret coefficients (K_B, K_F). For each group 175, 210, 245 and 280 kg/m³ dosages were determined as initial dosages, which were obtained by removing 30 percent of the cement content of control concretes with 250, 300, 350, and 400 kg/m³ dosages. Test concretes were obtained by adding GGBS to concretes in an amount equivalent to approximately 0%, 15%, 30%, 50%, 70%, 90% and 110% of cement contents of control concretes with 250, 300, 350 and 400 kg/m³ dosages. All specimens were moist cured for 7, 14, 28, 63, 119, 180 and 365 days before compressive strength testing.The test results proved that the compressive strength of concrete mixtures containing GGBS increases as the amount of GGBS increase. After an optimum point, at around 55% of the total binder content, the addition of GGBS does not improve the compressive strength. This can be explained by the presence of unreacted GGBS, acting as a filler material in the paste.     

Behaviour of hybrid fibre reinforced concrete beam–column joints under reverse cyclic loads

An experimental investigation was carried out to study the effect of hybrid fibres on the strength and behaviour of High performance concrete beam column joints subjected to reverse cyclic loads. A total of 12 reinforced concrete beams column joints were cast and tested in the present investigation. High performance concrete of M60 grade was designed using the modified ACI method suggested by Aïtcin. Crimped steel fibres and polypropylene fibres were used in hybrid form. The main variables considered were the volume fraction of (i) crimped steel fibres viz. 0.5% (39.25 kg/m³) and 1.0% (78.5 kg/m³) and (ii) polypropylene fibres viz. 0.1% (0.9 kg/m³), 0.15% (1.35 kg/m³), and 0.2% (1.8 kg/m³). Addition of fibres in hybrid form improved many of the engineering properties such as the first crack load, ultimate load and ductility factor of the composite. The combination of 1% (78.5 kg/m³) volume fraction of steel fibres and 0.15% (1.35 kg/m³) volume fraction of polypropylene fibres gave better performance with respect to energy dissipation capacity and stiffness degradation than the other combinations.     

Influence of water content on hardening and handling of a premixed calcium phosphate cement

Handling of calcium phosphate cements is difficult, where problems often arise during mixing, transferring to syringes, and subsequent injection. Via the use of premixed cements the risk of handling complications is reduced. However, for premixed cements to work in a clinical situation the setting time needs to be improved. The objective of this study is to investigate the influence of the addition of water on the properties of premixed cement. Monetite-forming premixed cements with small amounts of added water (less than 6.8 wt.%) were prepared and the influence on injectability, working time, setting time and mechanical strength was evaluated. The results showed that the addition of small amounts of water had significant influence on the properties of the premixed cement. With the addition of just 1.7 wt.% water, the force needed to extrude the cement from a syringe was reduced from 107 (± 15) N to 39 (± 9) N, the compression strength was almost doubled, and the setting time decreased from 29 (± 4) min to 19 (± 2) min, while the working time remained 5 to 6 h. This study demonstrates the importance of controlling the water content in premixed cement pastes and how water can be used to improve the properties of premixed cements.     

Continuous float–sink density separation of lump iron ore using a dry sand fluidized bed dense medium

A continuous separator based on float–sink density separation using a gas–solid fluidized bed dense medium was used to upgrade iron ore. The separator has three devices for (A) conveying floaters, (B) recovering floaters, and (C) conveying and recovering sinkers. The optimum speeds of these devices were investigated using density adjusted spheres of the diameter = 30 mm in the range of 2400–3300 kg/m³ in density increments of 100 kg/m³. A mixture of zircon sand and iron powder was used as the fluidized medium to adjust the fluidized bed density to produce a separation density = 2850 kg/m³, a typical separation density for lump iron ore wet separation. The recovery of the spheres as floaters or sinkers depended on the speed of the devices, because the recovery was affected by the number density of spheres directly under the feeder, the local fluidized bed density, and flow currents in the medium derived from the movement of the devices. The optimum speeds were determined to be 3.5 cm/s for (A), 2.0 rpm for (B) and 1.0 cm/s for (C), respectively. Continuous separation experiments were conducted on lump iron ore particles in the size range of +11.1–31.5 mm in the fluidized bed with medium density of 2850 kg/m³ and feed rate of 200 kg/h. Comparison of the feed rate and the recovery rate indicated that the feed and the recovery were in equilibrium after 10 min of operation. The experiments resulted in nearly perfect separation; 98.4% of the ore with density greater than 2850 kg/m³ was recovered. The Fe, Al and Si content of the feed ore particles (before the separation) and the floaters and sinkers (after the separation) was measured using inductively coupled plasma spectrometry. The separator produced an upgrade in iron content of 3.3 wt% and reduced the Al and Si content by 44%.