Blended Portland Cement Research Articles

Effect of substitution of blast-furnace slag by fired drinking water sludge on the properties of pozzolanic cement pastes

The effect of fired drinking water sludge (FDWS) as a mineral admixture on the physico-mechanical properties and the fire resistance of pozzolanic cement pastes has been investigated. Five blends of ordinary Portland cement, blast-furnace slag (GBFS) and FDWS were prepared. The Portland cement was fixed to 70 mass%, while granulated slag was replaced by 0, 3, 6, 9 and 12 mass% of fired sludge. The phase composition was identified using X-ray diffraction, thermal gravimetric analysis and differential scanning calorimetry. The results have shown an increase in the required water of standard consistency and elongation of setting times with increasing the fired sludge content. The bulk density has decreased with increasing the sludge content, while the compressive strength was enhanced at later ages for 3 and 6 mass% FDWS substitution. In addition, the specimen that contains 9 mass% FDWS gave the best firing resistance at high temperature, whereas Portland cement paste has been completely deteriorated at 800 °C.

Carbonation of ternary cementitious concrete systems containing fly ash and silica fume

Carbonation is quite a complex physical negative effect phenomenon on concrete especially in the ones containing ternary blends of Portland Cement, fly ash, and silica fume. Nine selected concrete mixtures were prepared with various water to cementitious materials’ ratios and various cementitious contents. The concrete mixtures were adapted in such a way to have the same workability and air content. The fresh concrete properties were kept near identical in slump, air content, and unit weight. The variation was in the hardened concrete mechanical properties of compression and tension strength. The carbonation phenomenon was studied for these mixes showing at which mixes of ternary cementitious content heavy carbonation attacks maybe produced. The main components of such mixes that do affect the carbonation process with time were presented.

Influence of the Ca/Si ratio of the C–S–H phase on the interaction with sulfate ions and its impact on the ettringite crystallization pressure

The effect of the Ca/Si ratio of the calcium–silicate–hydrate (C–S–H) phase on the interaction with sulfate ions is investigated for C–S–H phases (Ca/Si=0.83, 1.25, 1.50) and mortar samples of blended Portland cements. It is shown that leaching of calcium from C–S–H and portlandite affects the composition of the pore solution and contributes to the developing crystallization pressure of ettringite. Sulfate profiles show that sulfate binding before cracking is similar for different Ca/Si ratios whereas the highest expansion rates are observed for the mortars with the highest Ca/Si ratios. After leaching in sulfate solutions, the C–S–H samples have been characterized by 29Si MAS NMR, thermogravimetric analysis, and elemental solution analysis. Generally, the exposure to sulfate solutions results in decalcification of the C–S–H, which increases with decreasing Ca/Si ratio. The data are in good agreement with thermodynamic modeling, indicating that equilibrium is almost achieved in the leached systems. Finally, the expansion of mortar samples exposed to sulfate solutions was much less at lower Ca/Si ratios of the cement blends. This reduced expansion can be related to the decrease of the supersaturation of the pore solution with respect to ettringite at lower Ca/Si ratios of the C–S–H and in the absence of portlandite.

HIGH-PERFORMANCE CONCRETE WITH MECHANOACTIVATED BINDER

The paper examines the problems associated with production of high-performance concretes by using a general purpose blended Portland cement which is to be mechanoactivated and modified with an organomineral additive. The experiment conducted in accordance with a tri-factorial D-optimum design enabled to establish an influence of independent factors (х1 – content of microsilica in the binder - 5±5%; х2 – binder consumption in concrete - 450±100 kg/m3; х3 – specific area (Ssp) of Portland cement - 400±100 m2/kg) on physical and mechanical properties of concrete. It was established that the use of the mechanoactivated general purpose blended Portland cement with an organomineral additive (microsilica+C-3) makes it possible to obtain high-performance concretes which compression strength on the 28th day reaches 120 MPa.

Impact of anhydrite proportion in a calcium sulfoaluminate cement and Portland cement blend

Calcium sulfoaluminate (CSA) cement and ordinary Portland cement (OPC) blends are innovative binders. In comparison with OPC, these mixtures can reduce the environmental impact of cement production as well as increase the hardening speed. This article deals with the effects of calcium sulfate (anhydrite) percentage on hydration mechanisms, compressive strength and dimensional stability of binders containing 40% OPC. Calcium sulfate quantity is an essential parameter that can be used to control the hardening speed and dimensional stability. Mortars with 6·5% and 10% anhydrite present moderate compressive strength and expansion, whereas higher compressive strength and expansion are obtained with blends containing 17% and 20·5% anhydrite. These anhydrite proportions slow down the OPC and CSA clinker hydration kinetics but increase the ettringite proportion and stability.

Mechanical properties, durability, and life-cycle assessment of self-consolidating concrete mixtures made with blended portland cements containing fly ash and limestone powder

This paper reports the composition and properties of highly flowable self-consolidating concrete (SCC) mixtures made of high proportions of cement replacement materials such as fly ash and pulverized limestone instead of high dosage of a plasticizing agent or viscosity-modifying chemical admixtures. Self-consolidating concrete mixtures are being increasingly used for the construction of highly reinforced complex concrete elements and for massive concrete structures such as dams and thick foundation. In this study, by varying the proportion of portland cement (OPC), Class F-fly ash (F), and limestone powder (L), SCC mixtures with different strength values were produced, and the properties of both fresh and hardened concrete were determined. For a comprehensive analysis and quantification of emissions and global warming potential (GWP) from concrete production, life-cycle assessment (LCA) was employed. We find that high volume, up to 55% by weight replacement of OPC with F, or F and L produces highly workable concrete that has high 28-day and 365-day strength, and extremely high to very high resistance to chloride penetration along with low GWP for concrete production.

Strength and permeability properties of self-compacting concrete with cold bonded fly ash lightweight aggregate

This paper presents the results of an experimental study on the hardened characteristics of the self-compacting concretes made with cold bond fly ash lightweight aggregates. Binary and ternary use of fly ash (FA) and silica fume (SF) blends have been considered in the production of self-compacting cold bonded fly ash lightweight aggregate concretes (SCLWCs). For this, a total of 9 SCLWC mixtures were proportioned having constant water–binder ratio of 0.35 and the total binder content of 550kg/m3. The control mixture contained only Portland cement (PC) as the binder while the remaining mixtures having binary and ternary blends of PC, FA, and SF. Properties that include compressive strength and ultrasonic pulse velocity, chloride ion penetration, gas permeability, water absorption by total immersion and by capillary absorption were investigated at two curing ages of 28 and 56days. Test results have showed that incorporating the mineral admixtures enhanced significantly the permeability characteristics. Moreover, it was observed that the compressive strength of the SCLWCs with SF was much higher than those of the control concrete.

Characteristics of calcined natural zeolites for use in high-performance pozzolan blended cements

Two natural zeolites with different characteristics were calcined at various temperatures in order to improve the benefits provided by their use in blended cements as cement replacement material. Natural zeolites were firstly characterized for their crystallinity by X-ray diffraction analysis, specific surface area by nitrogen absorption, and pozzolanic activity by electrical conductivity method, before and after the calcination. In order to assess the performance of calcined natural zeolite as cement replacement material, blended Portland cement pastes and mortars with raw and calcined zeolites were tested for their water requirement, free lime content, pore size distribution and compressive strength. The experimental results indicated that calcined zeolites are more desirable with lower water requirement and higher strength performance as cement replacement material than the raw zeolites. Blended cement with calcined natural zeolite showed higher compressive strength performance, when compared to that with the raw zeolite due to decreased porosity and refined pore structure of the hardened cementitious system.

Hydration of quaternary Portland cement blends containing blast-furnace slag, siliceous fly ash and limestone powder

In this study the hydration of quaternary Portland cements containing blast-furnace slag, type V fly ash and limestone and the relationship between the types and contents of supplementary cementitious materials and the hydrate assemblage were investigated at ages of up to 182days using X-ray diffraction and thermogravimetric analysis. In addition thermodynamic modeling was used to calculate the total volume of hydrates. Two blast-furnace slag contents of 20 and 30wt.% were studied in blends containing fly ash and/or limestone at a cement replacement of 50wt.%. In all cases the experiments showed the presence of C–S–H, portlandite and ettringite. In samples without limestone, monosulfate was formed; in the presence of limestone monocarbonate was present instead. The addition of 5wt.% of limestone resulted in a higher compressive strength after 28days than observed for cements with lower or higher limestone content. Overall the presence of fly ash exerts little influence on the hydrate assemblage. The strength development reveals that amounts of up to 30wt.% fly ash can be used in quaternary cements without significant loss in compressive strength.

Strength and chloride resistance of the blended Portland cement mortar containing rice husk ash and ground river sand

In this paper, the strength and chloride penetration resistance of the blended Portland cement mortar containing rice husk ash (RHA) and ground river sand (GS) were studied. Portland cement type I (OPC) was partially replaced with RHA and GS and a blended of RHA and GS. The mortar mixtures were made with OPC containing 0–40 % of RHA and GS. RHA and GS with 3 % by weight retained on sieve No. 325 (opening 45 µm of sieve No. 325) were obtained using ball mill. The study includes compressive strength, rapid chloride penetration test, chloride ion diffusion coefficient and chloride penetration depth of mortars. Test results indicated that the use of RHA produced mortars with relatively high strength and excellent resistance to chloride penetration. However, the incorporation of GS reduced the strength and resistance to chloride penetration of mortars indicating that it asserted only the packing effect. The blend of equal portions of RHA and GS produced relatively high strength mortars with good resistance to chloride penetration which is probably due to the synergy of the pozzolanic effect of RHA and packing effect of GS.

Hydration and mechanical properties of cement/sludge/anhydrite gypsum system

Setting and hardening of fresh blends of ordinary Portland cement (OPC), fired drinking water treatment sludge (DWTS) and calcined anhydrite gypsum were investigated. Sludge or Portland cement was substituted with 5 wt%, 10 wt% or 15 wt% of anhydrite gypsum. These systems lead to the preparation of supersulfated cement. These blends were shown to possess both the advantages of gypsum (early hardening, high early strength and enhanced workability) and Portland cement (improved durability in moist conditions). The initial and final setting time, bulk density and compressive strength of cement pastes were measured. Differential scanning calorimetry, X-ray diffraction and Fourier transform infrared spectroscopy techniques were used to investigate the hydration products. Substitution of DWTS with 15% anhydrite accelerates the final setting time and increases the bulk density as well as the compressive strength. Substitution of OPC with 5% anhydrite gives the same results but extends the final setting time. It can be concluded that supersulfated cement can be prepared from samples with 10–15 wt% anhydrite substituted DWTS or from the sample with 5 wt% anhydrite substituted OPC.

PACKING ISSUE IN CEMENT BLENDING FOR SUSTAINABILITY DEVELOPMENTS - APPROACH BY DISCRETE ELEMENT METHOD

Common cement blending materials for concrete like fly ashes, blast furnace slag, silica fume, metakaolin and rice husk ash have been investigated experimentally as to their impact on concrete’s mechanical, physical and sustainability capabilities. Such efforts offer but case-related information on involved materials and used procedures. Generalizations will be difficult because also contradicting information is provided: a weak basis to guide further developments. Published research data on blends with inert components (carbon black) confirm fineness to be the leading parameter governing their mechanics. Experimental efforts revealing blending effects on durability issues are more scarce because of their complicated, laborious and time-consuming nature. Hence, generalization capabilities are even more restricted. An approach is therefore presented for studying cementitious materials in the virtual reality, employing the concurrent algorithm-based dynamic discrete element method (DEM), HADES. Hydration simulation of the simulated (blended) Portland cement grain mixture is thereupon accomplished with an extended version of the vector approach. Robotics-based pore delineation provides topological information, while geometric characterization of the pore networks is accomplished by star volume measurements. Topological and geometric parameters can be combined in a hydraulic model for durability estimation. This approach allows covering a wide range of parameters. This would render possible more systematic and economic development of such materials for sustainability purposes, among other things. The production stages (DEM and hydration simulation) and the analysis stages (pore delineation and topology and geometry assessment) are briefly outlined. Application of the methodology is illustrated on finer and coarser grained cements blended with rice husk ash produced with different fineness. The effects of the gap in grading on the pore network characteristics relevant for transport-based durability items are outlined.

Pore Structure Analysis of Portland Cement and Blended Portland Cements Cured under Hydrothermal Conditions

The pore structure of Portland cement pastes cured under different hydrothermal regimes was analyzed. Pore size distribution (PSD), hydraulic permeability coefficient (HK) and porosity (P) were found depending on temperature and steam pressure. With increasing hydrothermal characteristics, the pore structures degraded causing the depletion in compressive strength. Then, blast furnace slag (BFS) and silica fume (SF) were added to PC and cured under similar conditions. It was found that the pore structure was greatly improved. The effect of hydrothermal curing may be interpreted by the intensity and position of the peak, by the length and bimodal characteristic of PSD. The maximum concentration of pores of reference cement paste lies in the range 10 – 103 nm, and changes progressively to the size < 10 nm with increasing addition of BFS and SF. This behavior is attributed mainly to the presence of SF. Microstructure analysis shows hydrate products like needle CSH and CASH, which were stable under hydrothermal curing.

Eco-Cement Optimization Using Statistical Mixture Design Method

The statistical mixture design (SMD) method was used to find the optimum blending proportions of economical green cement by blending portland cement with fly ash, silica fume, and calcium carbonate. Twenty blends with different combinations of materials were tested on mortar mixtures to find the optimum and to analyze each. A graphical method was suggested for examining the mixture components on the response variables that included setting time and compressive strengths at 2, 7, and 28 days. The desirability function approach was used to calculate desired optimum blend of eco-cement at a minimum cost. The results from the experimental study were compared with the real-life situation of portland cement and pozzolanic portland cement analyzing on scanning electron microscope (SEM) for the microstructure. In mixture optimization, the SMD method is a useful tool to obtain a scientific solution instead of trial-and-error method with cost-effective mixture proportions.

Potential Use of Calcined Silt of Dam as a Pozzolan in Blended Portland Cement

This paper presents results of an experimental study which investigates the effect of industrial pozzolan made from calcined silt of dam at 750 °C for 5 h, on mechanical properties and durability of ordinary mortar, compared to the silica fume. Mortar specimens prepared with 5, 10 and 15 % of calcined silt to substitute cement were evaluated for their compressive and flexural strength, sulfate, acid and penetration of chloride ions resistance. The results were compared with ordinary mortar (without addition) and mortar containing 10 % of silica fume. The results obtained showed that the calcined silt of dam has a high potential to be used as a pozzolanic material, it improves the strength and the durability of mortar and compete the silica fume.

A modified ASTM C1012 procedure for qualifying blended cements containing limestone and SCMs for use in sulfate-rich environments

Blended Portland cements containing up to 15% limestone have recently been introduced into Canada and the USA. These cements were initially not allowed for use in sulfate environments but this restriction has been lifted in the Canadian cement specification, provided that the “limestone cement” includes sufficient SCM and that it passes a modified version of the CSA A3004-C8 (equivalent to ASTM C1012) test procedure run at a low temperature (5°C). This new procedure is proposed as a means of predicting the risk of the thaumasite form of sulfate attack in concretes containing limestone cements. The goal of the present study was to better understand how this approach works both in practice and in theory. Results from three different laboratories utilizing the CSA A3004-C8 test procedure are compared and analyzed, while also taking into account the results of thermodynamic modeling and of thaumasite formation experiments conducted in dilute suspensions.

Effect of Milling Process for Rice Husk Ash on Mechanical Strength of Blended Portland Cement Mortars

Nowadays, the reuse of waste products in the construction process is a priority research area. Several industrial and agricultural waste products have been investigated, such as fly ash, sugar cane bagasse ash and rice husk ash. This paper analyzes a very important aspect under intense discussion in the scientific community: the Rice Husk Ash (RHA) grinding process. This paper investigates a low carbon RHA with high pozzolanic reactivity produced under uncontrolled burning conditions. The compressive strength of mortar specimens prepared using both ground and natural RHA were tested for 3-56 days and the capillarity absorption was measured for mortars cured during 28 days. Very promising and interesting results were obtained using natural rice husk ash in the production of blended mortars.

Selected Properties of Cementitous Composites with Portland Cements and Blended Portland Cements in Extreme Conditions

The paper is focused on research of physico-mechanical properties of concretes with Portland-limestone cement, Blastfurnace cement and Portland-composite cement in comparisom with concrete with Portland Cement CEM I. Following physico-mechanical properties of concretes exposed to extreme conditions were tested: compressive strength, flexural strength, tensille splitting strength, velocity of propagation of ultrasonic pulse, dynamic elasticity modulus and density of hardened concrete. Following environments were used in tests: sulphates, magnesic ions, nitrates, gaseous CO2, high temperatures.

The capacity of ternary blends containing slag and high-calcium fly ash to mitigate alkali silica reaction

The efficiency of ternary blends containing high-calcium fly ash and slag in mitigating alkali-silica reaction (ASR) was evaluated. The concrete prism expansions showed that the ternary blends did not offer significant advantage over binary blends of portland cement and either of the individual material at the same total SCM content. The ability of a particular blend to mitigate ASR was related to its capacity to retain alkalis in its hydration products, as evaluated by an alkali leaching test. For the slag and fly ash used in this study, the capacity to retain alkalis increased with the ability of the blend to consume Ca(OH)2 during its pozzolanic reaction. For the blends investigated here, the alkali leaching test was more realistic than the accelerated mortar bar test in predicting the 2-year expansion of concrete prisms. The adopted alkali leaching test is proposed to be used as a tool to compare the efficacy of different cementing blends to mitigate ASR.

Ionic aqueous diffusion through unsaturated cementitious materials – A comparative study

The diffusion coefficient is a highly important parameter either as a durability indicator in the field of civil engineering or as an assessment criterion in the domain of nuclear waste disposal. In this paper we address the fundamental issue of the diffusion coefficient evolution with the water saturation level of cement-based materials. The study is comparing concretes and cement pastes cast with either blended cement or Portland cement. The analysis emphasizes the impact of the pore size distribution on the diffusivity as a function of the saturation degree.