Supplementary cementing materials in concrete: Part I: efficiency and design

Many solid industrial by-products such as siliceous and aluminous materials (fly ash, silica fume, slags, etc.) as well as some natural pozzolanic materials (volcanic tuffs, diatomaceous earth, etc.) may be characterized as supplementary cementing materials (SCM) as they exhibit cementitious and/or pozzolanic properties. Due to plenty of these materials and their large variations on physical and chemical composition, the development of a general design for their use in concrete is required. In this work, the concept of an efficiency factor is applied as a measure of the relative performance of SCM compared with Portland cement. Artificial materials of various compositions and some natural pozzolans were studied. Compressive strength and accelerated chloride penetration tests were performed. With regard to these characteristics, efficiency factors for these materials were calculated. A mix design strategy to fulfil any requirements for concrete strength and service lifetime was developed and it enables concrete performance to be accurately predicted.     

Supplementary cementing materials in concrete: Part II: A fundamental estimation of the efficiency factor

For comparing the relative performance of various supplementary cementing materials (SCMs: silica fume, fly ash, slag, natural pozzolans, etc.) as regards Portland cement, the practical concept of an efficiency factor may be applied. The efficiency factor (or k value) is defined as the part of the SCM in an SCM-concrete that can be considered as equivalent to Portland cement. In the present work, an alternative procedure for experimental determination of the k value is proposed, using the concept of the pozzolanic activity index. For the first time, also, the k value for equivalent strength was correlated with the active silica content of the SCM through analytical expressions. Artificial pozzolanic materials of various compositions and some natural pozzolans were studied. It was found and verified by experimental comparison that these expressions are valid only for artificial SCMs (fly ash, slag), whereas in the case of natural SCMs the k value is overestimated. Thus, knowing primarily the active silica content of the SCM, a first approximation of the k value can be obtained and, further, the strength of a concrete incorporating artificial SCM can be predicted.     

Fly ash effects: II. The active effect of fly ash

This paper examines the method for determining the hydration degree of cement clinker and the pozzolanic reaction degree of fly ash in the system of cement and fly ash. In the base, the active effect of fly ash is studied. The studied results show that the active effect includes two aspects: (1) Fly ash has stronger pozzolanic activity and can react with Ca(OH)₂, and (2) it can promote the hydration of cement. When the content of fly ash is less, its pozzolanic activity can exert well, but its promoting role to the hydration of cement is weaker. When the content of fly ash is more, it is less than its pozzolanic activity can be used, but its promoting role to the hydration of cement is stronger.     

Fly ash effects: III. The microaggregate effect of fly ash

In this paper, the microaggregate effect of fly ash is studied systematically by micromechanics, the hypothesis of center particle and pore size distribution. It is pointed out that the microaggregate effect is an important effect of fly ash. It is strengthened with the increase of content of fly ash, but weakened with age. At early age, fly ash cannot fine the pore structure. At late age, fly ash may fine the pore structure. However, in general, the fining role is only a relative fining role.     

Effect of temperature and aging on the mechanical properties of concrete: Part I. Experimental results

This paper reports the results of curing temperature and aging on the strength and elastic modulus and the Part II paper suggests a prediction model based on these experimental results. Tests of 480 cylinders made of Types I, V, and V cement+fly ash concretes, cured in isothermal conditions of 10, 23, 35, and 50 °C and tested at the ages of 1, 3, 7, and 28 days are reported. According to the experimental results, concretes subjected to high temperatures at early ages attain higher early-age compressive and splitting tensile strengths but lower later-age compressive and splitting tensile strengths than concretes subjected to normal temperature. Even though the elastic modulus has the same tendency, the variation of elastic modulus with curing temperature is not so obvious as compressive strength. Based on the experimental result, the relationships among compressive strength, elastic modulus, and splitting tensile strength are analyzed, considering the effects of curing temperature, aging, and cement type.     

Effect of temperature and aging on the mechanical properties of concrete: Part II. Prediction model

In Part I, empirical relationships between compressive strength and splitting tensile strength or elastic modulus with temperature and aging were proposed. This paper investigates new prediction models estimating splitting tensile strength and elastic modulus without knowing compressive strength. The prediction model is suggested on the basis of the equation that was suggested to predict compressive strength. The mechanical properties calculated by the model are compared with empirical results presented in Part I. To evaluate in-place applicability of the model, the empirical data on strength and elastic modulus of concrete cured at variable temperature are compared with the values estimated using the prediction model. The prediction model properly estimates the strength and elastic modulus of Types I and V cement concretes cured at constant and variable temperature conditions.     

Effect of steam curing on class C high-volume fly ash concrete mixtures

The effect of steam curing on concrete incorporating ASTM Class C fly ash (FA), which is widely available in Turkey, was investigated. Cement was replaced with up to 70% fly ash, and concrete mixtures with 360 kg/m³ cementitious content and a constant water/binder ratio of 0.4 were made. Compressive strength of concrete, volume stability of mortar bar specimens, and setting times of pastes were investigated. Test results indicate that, under standard curing conditions, only 1-day strength of fly ash concrete was low. At later ages, the strength values of even 50% and 60% fly ash concretes were satisfactory. Steam curing accelerated the 1-day strength but the long-term strength was greatly reduced. Setting time of fly ash-cement pastes and volume stability of mortars with 50% or less fly ash content were found to be satisfactory for standard specimens. In addition, for steam curing, this properties were acceptable for all replacement ratios.     

Effects of the incorporation of Municipal Solid Waste Incineration fly ash in cement pastes and mortars: I. Experimental study

This work falls within the scope of a general problem regarding the assessment of concrete manufactured from waste materials. The main objective is to study the long-term evolution of these materials during the leaching process, using the cellular automaton-based hydration model developed at the National Institute of Standards and Technology. The work is based on the analysis of mortars and cement pastes containing experimental waste: Municipal Solid Waste Incineration fly ash (MSWI fly ash). The study therefore aims to develop a methodology for assessing concrete manufactured from waste, and not to study a process or a formulation enabling the incorporation of the waste in concrete. The physical, chemical and mineralogical characteristics of MSWI fly ash were first analysed to introduce them into the model. A simplified quantitative mineralogical composition of the ash was proposed. The performance characteristics (setting times, compressive strengths, shrinkage, etc.) for mortars containing ash were then studied.     

Determination of the apparent activation energy of one concrete by calorimetric and mechanical means: Influence of a superplasticizer

An instrument has been developed to perform calorimetric tests on concrete in isothermal conditions using 0.11×0.22-m cylindrical samples. The purpose of this article is to determine the apparent activation energy of one concrete as a function of temperature (10, 20 and 40 °C) using this technique and to compare it with that obtained by a mechanical means in order to validate the hypothesis made in maturity measurements, according to which the apparent activation energy values are assumed to be equivalent. The two means give relatively similar results (with differences of the order of 3 kJ/mol). It also seems possible to use a single apparent activation energy value over the entire temperature range (10-40 °C). Lastly, the effect of a superplasticizer on the apparent activation energy is examined, and it appears that its role is relatively small in the case of the concretes studied here.     

An experimental study on strength development of concrete containing fly ash and optimum usage of fly ash in concrete

This paper presents a laboratory study on the strength development of concrete containing fly ash and optimum use of fly ash in concrete. Fly ash was added according to the partial replacement method in mixtures. A total of 28 mixtures with different mix designs were prepared. 4 of them were prepared as control mixtures with 250, 300, 350, and 400 kg/m³ cement content in order to calculate the Bolomey and Feret coefficients (K_B, K_F). Four groups of mixtures were prepared, each group containing six mix designs and using the cement content of one of the control mixture as the base for the mix design. In each group 20% of the cement content of the control mixture was removed, resulting in starting mixtures with 200, 240, 280, and 320 kg/m³ cement content. Fly ash in the amount of approximately 15%, 25%, 33%, 42%, 50%, and 58% of the rest of the cement content was added as partial cement replacement. All specimens were moist cured for 28 and 180 days before compressive strength testing. The efficiency and the maximum content of fly ash that gives the maximum compressive strength were obtained by using Bolomey and Feret strength equations. Hence, the maximum amount of usable fly ash amount with the optimum efficiency was determined.This study showed that strength increases with increasing amount of fly ash up to an optimum value, beyond which strength starts to decrease with further addition of fly ash. The optimum value of fly ash for the four test groups is about 40% of cement. Fly ash/cement ratio is an important factor determining the efficiency of fly ash.     

High-percentage replacement of cement with fly ash for reinforced concrete pipe

Fly ash is commonly used as a substitute for cement within concrete in various applications. Manufacturers of reinforced concrete products commonly limit the quantity of fly ash used to 25% or less by weight. Test cylinders with varying percentages of Class C (25-65%) and Class F (25-75%) fly ash and a water-reducing admixture (WRA) were created under field manufacturing conditions and tested for 7-day compressive strength. Seven-day compressive strength for the concrete/fly ash/WRA was found to be highest when the concrete mix included approximately 35% Class C or 25% Class F fly ash. However, substitution ratios of up to 65% Class C or 40% Class F fly ash for cement met or exceeded American Society for Testing and Materials (ASTM) strength requirements for manufacture of Class I, II and III reinforced concrete pipe (RCP).     

Porosity of recycled concrete with substitution of recycled concrete aggregate: An experimental study

In this paper, we present the experimental analysis of samples of recycled concrete (RC) with replacement of natural aggregate (NA) by recycled aggregate originating from concrete (RCA). The results of the tests of mechanical properties of RC were used for comparison with tests of mercury intrusion porosimetry (MIP), in which the distribution of the theoretical pore radius, critical pore ratio, the surface area of the concrete, threshold ratio and average pore radius were studied at ages of 7, 28 and 90 days. The results showed some variation in the properties of the RC with respect to ordinary concrete. Porosity increases considerably when NA is replaced by RCA. Additionally, a reduction in the mechanical properties of the RC is seen compared with ordinary concrete when porosity increases.     

Study of mineralogy and leaching behavior of stabilized/solidified sludge using differential acid neutralization analysis: Part I: Experimental study

In this work, differential acid neutralization analysis, chemical analysis of selected leachates and mineralogical study (XRD and SEM-EDS) are combined to investigate the relationship between mineralogy and leaching behavior of hydroxide sludge doped in Zn and Cr stabilized/solidified by hydraulic binders. The leaching behavior of stabilized hydroxide sludge is controlled by the dissolution of portlandite (pH ~ 12) followed by the dissolution of AFt/AFm and hydrogarnets (pH between 12 and 10) and finally the dissolution of ettringite and of the siliceous matrix of C-S-H (pH < 10). The zinc behavior is independent of the main components and is controlled by the dissolution of calcium hydroxizincate and its reprecipitation as hydroxyde or its adsorption on C-S-H. Chromium release is linked to the sulfate one due to a substitution in AFt/AFm phases.The proposed combination of tests is highly pertinent to establish the links between mineralogy and leaching behavior. Nevertheless, the hypotheses formulated are insufficient to implement a behavioral model to describe the leaching behavior.     

Prediction of compressive strength of fly ash concrete by new apparent activation energy function

A new prediction model using apparent activation energy is proposed to estimate the variation of compressive strength of fly ash concrete with aging. After analyzing the experimental result with the model, fly ash replacement content and water-binder ratio influence on apparent activation energy was investigated.According to the analysis, the model provides a good estimation of compressive strength development of fly ash concrete with aging. As the fly ash replacement content increases, limiting relative compressive strength and initial apparent activation energy increase. Concrete with water-binder ratio smaller than 0.40 gives nearly constant limiting relative compressive strength and initial apparent activation energy when analyzed with various water-binder ratios. However, concrete with water-binder ratio larger than 0.40 increases limiting relative compressive strength and initial apparent activation energy.     

Performance characteristics of high-volume Class F fly ash concrete

More than 88 million tonnes of fly ash is generated in India each year. Most of the fly ash is of Class F type. The percentage utilization is around 10 to 15%. To increase its percentage utilization, an extensive investigation was carried out to use it in concrete. This article presents the results of an experimental investigation dealing with concrete incorporating high volumes of Class F fly ash. Portland cement was replaced with three percentages (40%, 45%, and 50%) of Class F fly ash. Tests were performed for fresh concrete properties: slump, air content, unit weight, and temperature. Compressive, splitting tensile, and flexural strengths, modulus of elasticity, and abrasion resistance were determined up to 365 days of testing.Test results indicated that the use of high volumes of Class F fly ash as a partial replacement of cement in concrete decreased its 28-day compressive, splitting tensile, and flexural strengths, modulus of elasticity, and abrasion resistance of the concrete. However, all these strength properties and abrasion resistance showed continuous and significant improvement at the ages of 91 and 365 days, which was most probably due to the pozzolanic reaction of fly ash. Based on the test results, it was concluded that Class F fly ash can be suitably used up to 50% level of cement replacement in concrete for use in precast elements and reinforced cement concrete construction.     

Utilization of fly ash with silica fume and properties of Portland cement-fly ash-silica fume concrete

This paper reports the normal consistency, setting time, workability and compressive strength results of Portland cement-fly ash-silica fume systems. The results show that water requirement for normal consistency was found to increase with increasing SF content while a decrease in initial setting time was found. Workability, measured in term of slump, was found to decrease with silica fume content (compared to blends without silica fume). However, it must be noted that despite the reduction in the slump values, the workability of Portland cement-fly ash-silica fume concrete in most cases remained higher than that of the Portland cement control concrete. Furthermore, the utilization of silica fume with fly ash was found to increase the compressive strength of concrete at early ages (pre 28 days) up to 145% with the highest strength obtained when silica fume was used at 10 wt%. Moreover, scanning electron micrographs show that utilization of fly ash with silica fume resulted in a much denser microstructure, thereby leading to an increase in compressive strength.     

The effect of pozzolans and slag on the expansion of mortars cured at elevated temperature: Part I: Expansive behaviour

The expansive behaviour of heat-cured mortars containing pozzolans and slag was investigated. In most cases, the addition of any amount of these materials to the mixture typically reduced the long-term expansion, slowed the rate of expansion, and delayed the onset of expansion. However, the efficacy of a particular pozzolan or slag in controlling expansion may depend on its Al₂O₃ content. Metakaolin, which contains a high amount of reactive Al₂O₃, was the most effective at controlling expansion at relatively low cement replacement levels. Slag and fly ash, which are also sources of Al₂O₃, were also effective at suppressing expansion at higher replacement levels. Silica fume was less effective at controlling expansion at conventional replacement levels, and even at higher replacement levels expansion may only be delayed.     

The application of Raman spectrometry to the investigation of cement: Part II: A micro-Raman study of OPC, slag and fly ash

Various attempts to use Raman spectrometry to analyse the mineral phases in hydrated and unhydrated cement have been made and results were published on pure synthesized mineral phases as early as 1976. Limited investigations were reported in the past three decades on pure mineral cement phases, white cement and ordinary Portland cement (OPC) analysed with visible (VIS) excitation at 514.5 and 632 nm (mainly with normal Raman spectrometry) and near-infrared (NIR) excitation at 1064 nm (mainly Fourier Transform Raman Spectrometry — FT-Raman). Results were distinctly different for VIS and NIR lasers. Newman and co-workers assigned these differences to a fluorescence phenomenon. Previous work on the characterization of secondary cement materials (SCMs) by means of Raman spectrometry is even more limited. This work focused on the characterization of OPC, fly ash and slag, using ultraviolet-visible (UV-VIS), VIS and NIR excitation in micro-Raman spectrometry and the results obtained for OPC and fly ash will be compared with previously published results.     

High temperature behaviour of self-consolidating concrete: Microstructure and physicochemical properties

This paper presents an experimental study on the properties of self-compacting concrete (SCC) subjected to high temperature. Two SCC mixtures and one vibrated concrete mixture were tested. These concrete mixtures come from the French National Project B@P. The specimens of each concrete mixture were heated at a rate of 1 °C/min up to different temperatures (150, 300, 450 and 600 °C). In order to ensure a uniform temperature throughout the specimens, the temperature was held constant at the maximum temperature for 1 h before cooling. Mechanical properties at ambient temperature and residual mechanical properties after heating have already been determined. In this paper, the physicochemical properties and the microstuctural characteristics are presented. Thermogravimetric analysis, thermodifferential analysis, X-ray diffraction and SEM observations were used. The aim of these studies was in particular to explain the observed residual compressive strength increase between 150 and 300 °C.     

Effect of fine aggregate replacement with Class F fly ash on the mechanical properties of concrete

This paper presents the results of an experimental investigation carried out to evaluate the mechanical properties of concrete mixtures in which fine aggregate (sand) was partially replaced with Class F fly ash. Fine aggregate (sand) was replaced with five percentages (10%, 20%, 30%, 40%, and 50%) of Class F fly ash by weight. Tests were performed for properties of fresh concrete. Compressive strength, splitting tensile strength, flexural strength, and modulus of elasticity were determined at 7, 14, 28, 56, 91, and 365 days. Test results indicate significant improvement in the strength properties of plain concrete by the inclusion of fly ash as partial replacement of fine aggregate (sand), and can be effectively used in structural concrete.