Blended Cementitious Materials Research Articles

Evolution of Various States of Water in Blended Cementitious Materials

Low field NMR, as a nondestructure and noninvasive method was employed to study the evolution of various states of water in blended cementious materials added with fly ash during hydration from 1 day to 100 days. The relative content of water held in series of pores in cement matrix, e.g. capillary pore, mesopore and gel pore, was determined based on the quantitative relationship between transverse relaxation time, T2, and pore dimension. The results indicated that the relative content of chemically bound water was higher at long-term cure of 100 days compared with the neat cement paste. The water distributed in various pores was also influenced by the pozzolanic reactions between fly ash and calcium hydroxide. The gel water and mesopore water increased dramatically during the short-term age of 1 to 7 days in blended matrix, but then decreased gradually after 28 days, unlike that in pure cement paste. Due to the lower hydration degree in blended matrix, there was still amount of capillary water residual in paste to supply for the further hydration of fly ash.

Properties of cementitious materials in their dry state and their influences on viscosity of the cementitious pastes

Abstract The properties of cementitious materials in their dry state and their influences on viscosity of pastes were studied. The cementitious materials considered were Portland cement, fly ash, and ground granulated blast furnace slag (GGBFS). Both plain and blended mixes were tested, where plain mixes were made of a single material, while blended materials were made of the Portland cement blended with either fly ash or GGBFS. The properties tested for dry cementitious materials included the compression, recompression, swell indices, stiffness modulus, and coefficient of friction as well as the density and void ratio of gently consolidated bulk materials. Viscosity of the pastes, made with the plain and blended cementitious materials at a water-to-binder ratios (w/b) of 0.45 and 0.55 by weight, were measured. Correlations between the properties of the dry materials and viscosity of the pastes were analyzed. The results indicate that the size, shape and angularity of the cementitious materials greatly affect their dry-state properties as well as the flow behavior of the pastes. Cementitious materials that consolidate well in their dry state will produce a less viscous paste. A decrease in dry coefficient of friction and an increase in stiffness modulus will result in a decrease viscosity of the paste.

Improvements on Pozzolanic Reactivity of Coal Refuse by Thermal Activation

Today, coal refuse as industrial solid waste stockpiled on the ground is one of the greatest threats to the environment. One of the practical solutions to utilize this huge amount of solid waste is to activate the coal refuse and utilize it as substitution for portion of ordinary Portland cement. The key purpose of activation is to enhance the pozzolanic property of the coal refuse.Many scientists and engineers found that thermal activation is a practical approach on increasing pozzolanic property. For thermal activation, temperature and time are two important parameters which significantly determine the activation effect. In this paper, a systematic research has been conducted to seek for anoptimal solution for enhancing pozzolanic reactivity of the relatively inert solid waste-coal refuse in order to improve the utilization efficiency and economy benefit forconstruction and building materials.The mechanical property analysis shows that coal refusethat activated at 700°C to 800°C with 1 hour to 1.5 hours has much higher reactivity when compared with coal refuse activated at 500°C to 600 °C with 1 hour to 1.5 hours. And 28-dayscompressive strength value of prepared blended cementitious material containing 25% of the 700°C 1h activated coal refuse based pozzolanareaches 43.4MPa, which is higher than 28-days strength of OPC group as control.

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

Abstract 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.

Evolution of mineralogical phases produced during the pozzolanic reaction of different metakaolinite by-products: Influence of the activation process

In the past, different investigations have focused on waste containing kaolinite as an alternative source for recycled metakaolinite. However, it is well known that the activation conditions play an important role in the characteristics of the final product. This research presents an exhaustive study about the evolution of the mineralogical phases during the pozzolanic reaction of two metakaolinite by-products obtained from different activation processes: activation of paper sludge at lab scale (700 °C and 2 h) and at industrial scale (720–740 °C and 20–30 min) with a fluidized bed combustion system. It is shown that both metakaolinite by-products exhibit a different pozzolanic behavior, suggesting a direct influence on the subsequent performance of new blended cement matrices. The metakaolinite by-product obtained at lab-scale (MWL), generates an additional phase (carbonate/metakaolinite type structures) as predominant crystalline phase in the pozzolan/Ca(OH) 2 system up to 28 days of reaction. Stratlingite (C 2ASH 8) also appeared as minor stable phase after 7 days of reaction. On the other hand, the metakaolinite by-product from industrial process (MWI) favors the formation of C 4A C ¯ H 12 phase, whereas stratlingite was not identified.

Diffusivity and micro-hardness of blended cement materials exposed to external sulfate attack

Abstract Many degradation processes in cement based materials include the diffusion of one or more chemical species into concrete and consequent chemical reactions which alter the chemical and physical nature of the microstructure. External sulfate attack is mostly described by a coupled diffusion–reaction mechanism which leads to the decomposition of hardened cement constituents and cracking of the paste. This paper discusses the significance of diffusion properties and chemical changes in external sulfate attack in blended cement based composites. A method based on Particle Induced X-ray Emission (PIXE) was developed to measure the diffusion properties in a non-destructive test method. Quantitative Energy Dispersive Spectrometry (EDS) and micro-hardness technique were also used to study the chemical and mechanical changes from sulfate attack. Diffusion coefficients and rates of reaction were determined for paste and mortar mixtures, showing higher diffusion rates and lower hardness values in mortar compared to paste for control mixtures. Partial replacement of cement with fly ash improved the transport properties and reduced the level of damage in exposure to sulfate attack.

Study on optimization of hydration process of blended cement

To optimize the hydration process of blended cement, cement clinker and supplementary cementitious materials (SCMs) were ground and classified into several fractions. Early hydration process of each cementitious materials fraction was investigated by isothermal calorimeter. The results show fine cement clinker fractions show very high hydration rate, which leads to high water requirement, while fine SCMs fractions present relatively high hydration (or pozzolanic reaction) rate. Cement clinker fractions in the range of 8–24 μm show proper hydration rate in early ages and continue to hydrate rapidly afterward. Coarse cement clinker fractions largely play “filling effect” and make little contribution to the properties of blended cement regardless of their hydration activity (or pozzolanic activity). The hydration process of blended cement can be optimized by arranging high activity SCMs, cement clinker, and low activity SCMs in fine, middle, and coarse fractions, respectively, which not only results in reduced water requirement, high packing density, and homogeneous, dense microstructure, but also in high early and late mechanical properties.

Resistance of Hydrated Cement Paste to Acid Attack and Kinetics Analysis of Corrosion

The resistance of hydrated cement paste (HCP) to acid attack was investigated. Three groups of blended cementitious materials were designed, binary binder A (cement and slag), ternary binder B (cement, slag and silica fume), and quaternary binder C (polymer modified ternary binder). According to a series of designed experiments, acid resistance of HCP was tested by acid consumption, mass loss and corrosion depth of specimens. In the study, ternary binder B shows superior resistance to acid attack. The advantage of polymer modification is unobvious. Furthermore, the variability of acid corrosion depth d with time t was analyzed specially for the foundation of degradation model. Kinetics equation of acid corrosion was established in form of d=K•tn to predict HCP corrosion depth at specific age, which provides available references for durability analysis and engineering design of concrete structures.

Blended systems with calcium aluminate and calcium sulphate expansive additives

The high alumina cements were ground together with special sulphate–lime sinter to produce an expansive additive to Portland cement. This expansive additive in the environment of hydrating cement transforms into the hydrated calcium sulfoaluminate phase known as ettringite at “right time” to give the expansion before the early hardening process is completed. The studies were focused at first on the synthesis of the sulphate–lime sinter and subsequently on the mixture proportions between the basic Portland cement, calcium aluminate cement and sulphate–lime component giving the compensation of shrinkage or expansion effect during the hydration process. The measurements of volume changes of cementitious materials thus produced, followed by the compressive strength tests, rate of hydration determination, phase composition studies and microstructure of hydration products observations have been carried out to find the optimum proportions of blended cementitious material, as the controlled expansion and hardening are concerned.

Transport properties in metakaolin blended concrete

One of the approaches in improving the durability of concrete is to use blended cement materials such as fly ash, silica fume, slag and more recently, metakaolin. By changing the chemistry and microstructure of concrete, pozzolans reduce the capillary porosity of the cementitious system and make them less permeable to exterior chemical sources as well as reducing the internal chemical incompatibilities such as alkali–silica reaction. This paper presents the results of a study on the transport properties and durability characteristics of concrete containing different levels of metakaolin. Water penetration, gas permeability, water absorption, electrical resistivity, chloride ingress, and alkali–silica reaction potential were studied and their inter-relationships discussed. Results show that substituting optimum levels of metakaolin improves different aspects of the transport properties and durability performance. At 15% replacement level, compressive strength increased by 20%, while the water penetration, gas permeability, water absorption, electrical resistivity and ionic diffusion had improvements of up to 50%, 37%, 28%, 450%, and 47%, respectively and the 28-day ASR expansion for this mix was reduced as much as 82%. The minimum replacement level required for mitigating ASR and the relationship between physical and chemical effects of metakaolin were discussed.

Correlation of Reaction Products and Expansion Potential in Alkali-Silica Reaction for Blended Cement Materials

This article will review how blended cements are effective in controlling the alkali-silica reaction (ASR) expansion by changing the chemical reactions, as well as improving the transport properties of concrete. Several models have been proposed to describe the mechanism by which ASR can damage cement-based materials. Nonetheless, the effect of blended cements on the morphology and chemical composition of reaction products needs better understanding. In this study, experimental data from the ASTM C1567 test method and microstructural studies, including an environmental scanning electron microscope (ESEM) and quantitative energy dispersive spectrometer (EDS), were used to develop a physico-chemical model based on the properties of different silicate glass structures. One type of reactive aggregate and several fly ashes with various properties were used. An analysis of the number of bridging and nonbridging oxygens in the gel network in acidic and basic environments provided further insight into ASR products. The distinction between “safe” and “unsafe” reaction products was discussed with the formation of smooth gels with Na-Si-O phase versus the dispersed platelets with Ca-Na-Si-O composition.

Multi-parameter study of external sulfate attack in blended cement materials

A conventional solution in reducing the potential damage in concrete structures from external sulfate attack is to partially replace the Portland cement with appropriate fly ash. Presently, the compatibility of fly ash as a remedial cement substitution is based on empirically developed ASTM classifications. With proper testing techniques and multi-parameter approaches, one can better correlate the properties of blended cements with the expected level of damage. In this paper, parameters affecting the sulfate resistance of concrete are reviewed and the modifications to conventional expansion tests are discussed. The role of fly ash chemical composition on the level of damage was studied experimentally at macro and micro-scales. The linear expansions were determined both in paste and mortar systems using standard size and modified size specimens. Microstructural studies using ESEM and quantitative EDS were used to characterize the nature of reaction products and fronts. Statistical analysis of data indicated that the sulfate resistance of cementitious materials is significantly influenced by the chemical composition and the transport properties of the system which can be improved by appropriate fly ash substitution. It is also demonstrated that the study of these mechanisms can be expedited using modified size specimens.

Packing density of cementitious materials: measurement and modelling

Packing density has great effect on the performance of a concrete mix. However, little research has been carried out on the packing density of cementitious materials owing to the lack of an established measurement method. Herein, a new method, called the wet packing method, is presented. With this method, the packing densities of blended cementitious materials, consisting of ordinary Portland cement (OPC), pulverised fuel ash (PFA) and condensed silica fume (CSF), were measured. The results verified the theory that the packing density could be significantly increased by blending two or even three cementitious materials together. Comparison between the measured results and the predicted values by three existing packing models, together with some additional tests, revealed that in the presence of a third-generation superplasticiser, the packing density of CSF is dependent on the lime content. When the lime-containing OPC and PFA contents are low, the CSF particles would flocculate and pack rather loosely, but at higher OPC and PFA contents, or with lime added, the CSF would pack to a higher density. With the effect of lime accounted for, very good agreement between the measured results and the predictions by the packing models was achieved.

Packing density of cementitious materials: part 1—measurement using a wet packing method

The packing characteristics of the cementitious materials have great influence on the performance of a concrete mix, but there is so far no generally accepted method of measurement. Herein, a new method, called the wet packing method, is developed. It mixes the cementitious materials with water and then measures the apparent density and voids content of the resulting mixture at varying water/cementitious materials ratio to characterise the packing behaviour of the cementitious materials. Trial mixing and testing revealed that the mixing procedure is crucial to the success of the test method. To ensure thorough mixing within a reasonable time, a special mixing procedure is adopted. Using this method, the packing characteristics of pure cement and blended cementitious materials under different conditions have been measured. Based on the results so obtained, it is advocated that the packing density and water demand should be measured directly using a wet packing method rather than indirectly by any consistence test because the water content at any preset consistence is not necessarily the same as the minimum water content needed to fill up the voids. Some useful applications of the new method are illustrated in Part 2 of this paper.

Effect of incorporating ferroalloy industry wastes as complementary cementing materials on the properties of blended cement matrices

The main purpose of this study is to evaluate the characteristics of two by-products obtained during ferroalloys production, SiMn slag and Mn oxide filter cakes, and their possible use as complementary cementing materials for commercial Portland cement manufacturing, considering 5% and 15% additions. The results obtained have revealed that by-product characteristics make them suitable to be added to blended cement production processes since they fulfill the European regulations for the chemical, physical and mechanical requirements. Regarding the Mn oxide filter cakes use, a strength loss has been detected in blended cement mortars after a 90 days curing, although pore size distribution in this case is similar to that of a control mortar.

Optimization of SO3 content in blended cementitious materials

Experimental investigation was conducted on the effects of gypsum types and SO3 content on the fluidity and strengths of different cementitious systems. The experimental results show that influences of gypsum in various cementitious materials are different. For cementitious materials blended with various proportions of slag-fly ash and 5% gypsum content, influences of gypsum and calcined gypsum on the fluidity and flexural/compressive strength are similar. It is revealed that “combination effect” and “synergistic effect” of slag and fly ash play an important role during hydration. For cementitious materials with 45% clinkers, 30% slag, 20% fly ash and 5% limestone, the optimized SO3 contents in gypsum and calcined gypsum are 3.13% and 3.51% respectively and the optimized gypsum content is 6.5%. While both of them are blended, the optimum ratio of gypsum to calcined gypsum is 40%:60% (total gypsum content 6.5%), correspondingly the optimum ratio of SO3 is 19.3%:32. 4%.

Fundamental aspects of cement solidification and stabilisation

Cement matrix materials intended for immobilisation vary considerably in their formulation. It is often economically and technically advantageous to add blending agents: e.g. slag and fly ash. These affect the chemical, mineralogical and microstructural constitution of the system. However, blending agents react slowly with the result that the physicochemical properties of the matrix are time dependent. This affects especially conclusions which might be reached from accelerated short-term leach tests: the intrinsic performance of blended cement matrices improves with maturation. The matrix interactions with waste species are characterised using chromium, molybdenum, uranium and arsenic as examples. Formation of relatively insoluble precipitates, by reaction of waste species with cement components, provides chemical control over leach rates and accounts for many of the observed retentive properties. It is concluded that further focused research is needed to characterise the future performance of cement matrices in open system environments, where chemical exchanges occur between cements and the disposal environment.

High-resolution Transmission Electron Microscopy studies of microstructures in blended cement pastes

In providing high resolution analysis of morphology, composition and crystal structure in cement-based pastes, TEM has played an important role and some essential features of the materials have been observed. Because of both improved properties and economic advantages, blended cement materials have been widely developed. However, there is relatively little report with respect to the microstructures in the blended systems containing more than two source materials. In an effort to derive a more complete picture of structural development in hydration products of blended grouts and to have a better understanding of effects of source materials on the resulting products, we applied TEM/EDXA techniques to study the microstructures of cement/fly-ash/slag/limestone blended grout samples. Four starting materials and hydrating products were evaluated. The grout samples at various hydration stages were quenched into acetone solution to stop the hydration reaction. The thin sections for TEM/EDXA were prepared by using an ultramicrotome thinning technique.

Municipal wastewater sludge as cementitious and blended cement materials

The potential for using wastewater sludge in combination with limestone to produce cementitious building materials is investigated. A ground mixture of the raw materials was incinerated to produce the cement clinker. The effects of raw materials mix compositions, incineration temperatures and durations on various properties of the cement were examined. The experimental results show that under controlled incineration, it is possible to produce the so-called ‘Bio-cement’ from wastewater sludge that would satisfy the strength requirements for masonry cement. When being used as a partial replacement material for portland cement, the Bio-cement can replace up to 30% by weight of ordinary portland cement without deteriorating the mortar strength. Blended cement with up to 10% replacement level not only shows higher strength than control portland cement, it also exhibits a higher rate of strength development at early ages. This paper presents properties of the cements as well as their strength characteristics.

Fiber Reinforced Alkali Activated Blended Cement Materials

AbstractRecently there has been renewed interest in the use of alkali activation to increase the rate of strength development in blended cements. The objective of this study was to examine the advantages-disadvantages of using alkali activated blended cement materials with fiber reinforcing. There are advantages of the rapid set for certain applications.