Showing papers in "Cement & Concrete Composites in 2001"

Metakaolin and calcined clays as pozzolans for concrete: a review

Abstract: The utilisation of calcined clay, in the form of metakaolin (MK), as a pozzolanic material for mortar and concrete has received considerable attention in recent years. This interest is part of the widely spread attention directed towards the utilisation of wastes and industrial by-products in order to minimise Portland cement (PC) consumption, the manufacture of which being environmentally damaging. Another reason is that mortar and concrete, which contain pozzolanic materials, exhibit considerable enhancement in durability properties. This paper reviews work carried out on the use of MK as a partial pozzolanic replacement for cement in mortar and concrete and in the containment of hazardous wastes. The literature demonstrates that MK is an effective pozzolan which causes great improvement in the pore structure and hence the resistance of the concrete to the action of harmful solutions.

The ITZ in concrete – a different view based on image analysis and SEM observations

Abstract: The traditional picture of the ITZ in concrete involves an approximately 30 μm zone around each aggregate, within which the porosity increases as the aggregate interface is approached. The results of the writers' extensive image analysis investigations, and examinations of SEM specimens from various concretes provide a very different picture. While the “wall effect” excluded much of the ground cement from the vicinity of the aggregates, the great increases in pore content within a few μm of the aggregate, up to approximately 30% porosity, that have been reported by others, are not found. On average, only modestly higher porosities are observed within the ITZ than in the bulk paste. This is true even in the innermost areas immediately adjacent to the aggregates. In part, the extra space produced by the wall effect is filled in by CH deposits, many of which are anchored directly on the surfaces of aggregates and are essentially non-porous. Strong indications exist that the ITZ contains as high a proportion of C–S–H per unit volume as the bulk paste; thus some of the extra space that was created by the wall effect is filled in by through-solution deposits of C–S–H derived from elsewhere in the system. It is considered that the structure of the ITZ in ordinary concretes is not different enough from that of the bulk cement paste to provide any basis for significant effects on permeance or mechanical properties.

Effect of metakaolin on creep and shrinkage of concrete

Abstract: The effect of metakaolin (MK) on the creep and shrinkage of concrete mixes containing 0%, 5%, 10%, and 15% MK has been investigated. The results showed that the early age autogenous shrinkage measured from the time of initial set of the concrete was reduced with the inclusion of MK, but the long-term autogenous shrinkage measured from the age of 24 h was increased. At 5% replacement level, the effect of MK was to increase the total autogenous shrinkage considered from the time of initial set. While at replacement levels of 10% and 15%, it reduced the total autogenous shrinkage. The total shrinkage (autogenous plus drying shrinkage) measured from 24 h was reduced by the use of MK, while drying shrinkage was significantly less for the MK concretes than for the control concrete. The total creep, basic creep as well as drying creep were significantly reduced particularly at higher MK replacement levels. Compared with estimated values by the CEB 90 model, total creep of all concretes was overestimated, especially in the mixes containing the higher levels of MK. For basic creep, estimates for low levels of MK were acceptable but, for the higher levels, creep was overestimated.

Microcracking and strength development of alkali activated slag concrete

Abstract: Alkali activated slag concrete (AASC) is made by activating ground granulated blast furnace slag with alkalis without the use of any Portland cement. This study investigates the level of microcracking which occurs in AASC when subjected to various types of curing regimes. The corresponding compressive strength developments of AASC were monitored. The level of microcracking were measured using three different types of tests: (1) frequency and size of surface cracks using crack-detection microscope (2) water sorptivity tests measuring absorption of water by capillary attraction and (3) mercury intrusion porosimetry (MIP) tests which measured the pore size distribution of AASC and AAS pastes (AASPs). The results show that the lack of moist curing of AASC increased the level of microcracking measured using all three different tests mentioned above. The strength development of AASC is also significantly reduced by lack of moist curing.

New lightweight composite construction materials with low thermal conductivity

Abstract: This paper presents an initial investigation on the use of a new lightweight construction material, composed of cement, sand and fiber of waste from young coconut (Cocos nucifera) and durian (Durio zibethinus). Thermal conductivity, compressive strength and bulk density were investigated. The experimental investigation reveals that the addition of these fibers reduces the thermal conductivity of the composite specimen and yield a lightweight. The composite satisfies the basic requirement of construction materials, and they could be used for walls and roofs. Thus, the potential for development, therefore, seems to be very promising. Finally, apart from saving energy consumption for the building, the proposed materials offer an alternative option to dispose waste of fruit industry.

Increasing concrete durability with high-reactivity metakaolin

Abstract: High-reactivity metakaolin (HRM) is a manufactured pozzolan produced by thermal processing of purified kaolinitic clay. Field performance and laboratory research of concrete containing HRM have demonstrated its value for bridge decks, bridge deck overlays, industrial flooring, high-strength concrete and masonry products. This paper discusses laboratory evaluations to assess the long-term performance of concrete containing HRM produced in North America for resistance to chloride penetration and reduction in expansion due to alkali-silica reactivity. Bulk diffusion testing indicated that HRM substantially reduced chloride ion penetration in concrete with w/cm of 0.30 or 0.40. Reductions in diffusion coefficients compared to control specimens were of the order of 50% and 60% for concrete with 8% and 12% HRM, respectively. Also, the performance of the concrete containing 8% or 12% cement replacement with HRM showed improved performance versus merely reducing the w/c from 0.4 to 0.3. Such reductions can be expected to have a substantial impact on the service life of reinforced concrete in chloride environments. Expansion tests on concrete prisms containing reactive aggregates showed that 15% HRM can prevent deleterious expansion due to alkali-silica reactivity (ASR). The mechanism of control is likely linked to the substantial reduction in pore solution alkalinity seen in pastes containing 20% HRM in comparison to the control specimen which contained no supplementary cementing materials. However, the reduction was not large enough to depassivate steel reinforcement.

A study of ground coarse fly ashes with different finenesses from various sources as pozzolanic materials

Abstract: The aim of this study is to evaluate the properties of ground coarse fly ashes, from five sources in Thailand, the shapes, sizes, and chemical compositions of which are completely different. Coarse fly ash was fractionated by an air classifier and ground into three different finenesses ranging from median particle sizes of 1.9–17.2 μm. Physical and chemical properties of the Portland cement and the fly ashes were investigated. Mortar cubes of 5 cm were cast with 20% replacement by weight of Portland cement with ground coarse fly ash. The compressive strengths of the fly ash–cement mortars were determined and compared with the control mortar. The results revealed that the degree of pozzolanic reaction, as determined using compressive strength, of coarse fly ash increased when its fineness was increased by grinding. The strength activity indices of the original fly ash–cement mortars at the curing ages of 7 and 28 days were in the range of 69–82% and 76–90%, respectively. When the particle size smaller than 9 μm of ground coarse fly ash was used, the strength activity index achieved was over 100% of that of the control within 28 days. The results also showed that the fineness of fly ash, not the chemical composition, was the major factor affecting the strength activity index of ground coarse fly ash–cement mortar.

Pore size distribution and compressive strength of waste clay brick mortar

Abstract: This paper reports the results of an investigation of the pore size distribution of mortar that contains varying amounts of ground brick from different European brick types. Clay brick deriving from four European countries was ground to roughly cement fineness and used to partially replace cement in quantities of 0%, 10%, 20% and 30% in standard mortars. The pore volume, pore size distribution, threshold radius and strength of these mortars were tested for curing periods of up to one year. The presence of ground brick (GB) alters significantly the compressive strength of mortar and this is attributed to both the dilution effect and production of additional C–S–H gel from reaction of GB with CH. The additional C–S–H gel refines the pore size distribution of the mortar and this is reflected in compressive strength values obtained for these mixes. A critical relationship between threshold radius and compressive strength is also observed.

Mix proportioning of high performance concrete

Abstract: High performance concrete (HPC) is that concrete which meets special performance and uniformity requirements that cannot always be achieved by conventional materials, normal mixing, placing and curing practices. Special performance requirements using conventional materials can be achieved only by adopting low w/c, which necessitates use of high cement content. But judicious choice of chemical and mineral admixtures can reduce the cement content and this results in economical HPC. However, the effect of a mineral admixture on the strength of concrete varies significantly with its properties and replacement levels. Mix proportioning methods of normal concrete cannot adequately account for the large variations in the properties of ingredients. This paper presents a modified mix design procedure, which utilises optimum water content and the efficiency factor of mineral admixture. Results of the experimental investigations on mixes using the modified mix design are presented.

The influence of metakaolin and silica fume on the chemistry of alkali-silica reaction products

Abstract: This investigation studies the influence of two mineral admixtures, silica fume (SF) and high-reactivity metakaolin (HRM), on the chemistry of alkali–silica reaction (ASR) products Four different mortar bar mixes containing different combinations of high-alkali cement, alkali–inert dolomitic limestone, reactive Beltane opal, HRM, and SF were prepared and stored in a 1 N NaOH solution at 80°C (ASTM C 1260) for 21 days Expansion of bar specimens was measured, and chemical analysis was performed at different ages using X-ray spectra and maps Test results confirmed that HRM and SF significantly reduce expansion due to ASR In addition, X-ray microanalysis showed that calcium content increases with time in ASR products Furthermore, it was found that as ASR proceeded the calcium content of reaction products increased proportionally as the silica content decreased

Image analysis and mathematical morphology for civil engineering materials

Abstract: The scope of this paper is to present the main tools of image analysis to investigate materials and, specially, civil engineering ones. First the acquisition methods are described. The different operators for filtering, segmentation and binary image processing are presented and illustrated on different images. The influence of the observation field on these operators and the bias correction is also introduced. Then the problem of the parametrical characterization is presented: stereological parameters and functions related to size distributions, dispersion and anisotropy. Finally, the model methods based on image analysis are recalled. Some annexes illustrate this paper to precise main basic notions to understand the morphological tools.

Uniformity of in-situ properties of self-compacting concrete in full scale structural elements

Abstract: Inadequate homogeneity of the cast concrete due to poor compaction or segregation may dramatically lower the performance of mature concrete in situ. To ensure adequate compaction and facilitate placement of concrete in structures with congested reinforcement and in restricted areas, self-compacting concrete (SCC) has been developed. Considering the highly flowable and self-levelling nature of the SCC, there are general concerns that segregation and settlement may occur during its transport and placing. This study was designed to provide information on uniformity of in situ properties of SCC mixes in practical structural columns and beams and to compare results with those of properly compacted conventional concrete. The in situ concrete properties were assessed by testing cores for in situ strength, pull-out of pre-embedded inserts and rebound hammer number for near-surface properties. The results indicated that there were not significant differences in uniformity of in situ properties between the SCC mixes and the corresponding well compacted conventional mixes.

Strength and durability aspects of calcined kaolin-blended portland cement mortar and concrete

Abstract: Economic and sustainability arguments require carefully assessing the potentialities of indigenous resources for the production of mortar and concrete for the construction industry. In Vietnam, significant efforts should be bestowed on urban development, coastal protection and harbour construction works. In a joint Vietnamese-Dutch co-operation program, the practical use for this purpose of relevant resources in Northern Vietnam is assessed experimentally. This paper concentrates on kaolin, which is widely available in this region. The key issues this paper is dealing with are the effects of partial replacement of Portland cement by calcined kaolin in mortar and concrete on compressive strength as well as on durability characteristics of mortar and concrete mixes pertinent to the coastal environment. Workability measures are also mentioned. Data are therefore presented on compressive strength development over a maximum curing period of 180 days of mixes in which the water to binder ratio was varied between 0.40 and 0.53. Moreover, partial replacement was considered in the range from 0% to 30% by weight. The results of this study render possible the assessment of optimum replacement percentages of Portland cement by calcined kaolin, and the associated strength gain. Additionally, this paper reports on the performance aspects of similarly blended mortar and concrete specimens stored for a period of one year in a low concentration of a sodium sulfate solution. It could be concluded that a strength gain due to blending will be accompanied by improved durability in this environment.

Considerations in image analysis as applied to investigations of the ITZ in concrete

Abstract: A number of considerations are discussed with regard to the study of the Interfacial transition zone (ITZ) in concrete by image analysis of backscatter SEM images. These include selection and sampling of the concrete, selection of individual aggregates for the ITZ measurements, and design and positioning of individual sampling units around the chosen aggregates. Emphasis is placed on the importance of analyzing the lateral variation in properties around the aggregate as well as variation in mean composition with distance from the aggregate. Statistical considerations that can be applied to the interpretations of the results are illustrated.

Differential scanning calorimetry study of ordinary Portland cement paste containing metakaolin and theoretical approach of metakaolin activity

Abstract: This paper aims to investigate the hydration and pozzolanic reactions in cement pastes with different levels of metakaolin replacement, using differential scanning calorimetry (DSC) and theoretical analysis based on reaction stoichiometry. It was found that the DSC technique could follow the hydration process quantitatively by measuring the peak temperature and enthalpy corresponding to decomposition of hydration products, as functions of age. The pozzolanic process can also be followed from the measurements of the changes in the amount and the nature of amorphous material in the paste and the change of the amount of calcium hydroxide. In addition, it was confirmed that a theoretical approach using reaction stoichiometry could give a good estimation of the concentration of calcium hydroxide in a metakaolin concrete.

Transition zone studies of new-to-old concrete with different binders

Abstract: The weak transition zone between new and old concrete controls many properties of repaired concrete. The transition zone between aggregates and cement pastes of normal concrete has been studied by a number of researchers. But to date, there is little information available about the interfacial zone between new and old concrete. In this paper, major properties of the transition zone between new and old concrete with different binders were studied by using both scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The bond strength was also investigated. The test results show that the binder is a vital factor, which affects the morphology (size and shape), mineralogy and the microstructure of the transition zone in repaired concrete.

Compatibility of repair mortars with concrete in a hot-dry environment

Abstract: Strengthening, maintenance and repair of concrete structures are becoming more recognised in the field of civil engineering. There is a wide range of repair mortars with varying properties, available in the market and promoted by the suppliers, which makes the selection of the most suitable one often difficult. A research programme was conducted at Leeds University to investigate the properties of cementitious, polymer and polymer modified (PMC) repair mortars. Following an earlier publication on the intrinsic properties of the materials, this paper presents results on the compatibility of these materials with concrete. The dimensional stability is used in this study to investigate the compatibility of the repair mortars and the parent concrete. Composite cylindrical specimens (half repair mortar/half concrete) were prepared and used for the measurements of modulus of elasticity and shrinkage. The results of the different combined systems were obtained and compared to those calculated using a composite model. The variations between the measured and calculated values were less than 10%. The paper attempts to quantify the effect of indirect differential shrinkage on the permeability and diffusion characteristics of the different combined systems.

Image analysis for the automated study of microcracks in concrete

Abstract: An image analysis technique for the automated detection and quantification (at the mesoscopic scale) of microcracks in cement-based materials is described. In order to highlight microcracks and other microdefects, the surface of the material is impregnated with a red or a fluorescent dye. Observations of the polished sample are carried out using an optical microscope. The image analysis algorithm developed for the segmentation of the microcracks includes a pretreatment of the color image, an automatic thresholding carried out on the gray level histogram and a treatment of the binary image. The resulting image is then treated using a shape analysis and edge corrections. The characteristics of the crack network are quantitatively determined using classical stereological methods. The technique enables the user to draw maps of the sample crack network over an area of several tens of square centimeters. Results obtained for undamaged and mechanically loaded samples are presented.

Reuse of spent catalyst as fine aggregate in cement mortar

Abstract: This study examined the feasibility of reusing spent zeolite catalyst, after fluidized catalytic cracking, as a substitute for fine aggregate (sand) in cement mortars. The tested result shows that spent catalyst can replace up to 10% of fine aggregate without decreasing the mortar strength. In fact, the substituted mortars show higher compressive strength than the unsubstituted samples. The flowability of the fresh mortars decreases with increasing substitution level and the mortars incorporated with spent catalyst show less bleeding. In the hardened state, the water absorption of the resulting mortar increases with longer curing age, higher substitution level and smaller water-to-cement (W/C) ratio. Toxicity characteristic leaching procedure (TCLP) analysis confirms that the spent catalyst meets the standard, and thus should be classified as general non-hazardous industrial waste.

Effect of environmental conditions on the properties of fresh and hardened concrete

Abstract: The effect of varying environmental conditions, at the time of casting on the properties of fresh and hardened concrete was evaluated. The influence of air temperature, wind velocity, and relative humidity on plastic shrinkage, compressive strength, pulse velocity and pore structure of concrete was investigated. Results indicate that exposure conditions at the time of casting significantly affect plastic shrinkage of concrete. As expected elevated temperature affected porosity, compressive strength, and pulse velocity of concrete. Casting of concrete at elevated temperature decreased its compressive strength. Similarly, the pulse velocity of concrete cast at 45°C was less than that of cast at 30°C. The volume of total pores in the concrete specimens cast at 45°C was more than that of cast at 30°C. The lower pulse velocity and increased pore volume in the concrete cast at 45°C than that cast at 30°C may be attributed to the coarse pore structure formed in the former than the latter. Other weather parameters, such as relative humidity and wind velocity, also influence the properties of fresh and hardened concrete.

Improved model for plate-end shear of CFRP strengthened RC beams

Abstract: In case of RC members strengthened by means of externally bonded reinforcement, a premature failure can be detected in addition to the conventional modes of failure observed in RC unstrengthened beams. The premature failure occurs mainly due to both shear and normal stresses induced in either the external reinforcement–concrete interface or at the level of steel reinforcement. This research is part of a complete programme aiming to set up design formulae to predict the strength of CFRP strengthened beams, particularly when premature failure through laminates-end shear or concrete cover delamination occurs. Series of RC beams were strengthened with carbon-fiber-reinforced plastic (CFRP) laminates and tested to estimate the extent of the applicability of the formulae proposed by the authors, as well as to study the influence of the layout of the external reinforcement in terms of unsheeted length (the distance between CFRP laminates-end and the nearer support) and cross-sectional area, on the behaviour of strengthened beams. The predictions using the proposed formulae are compared with the obtained experimental results, as well as with the calculated design limit states. The interfacial shear stress and the maximum deflection corresponding to the predicted values at maximum and service loads are also studied.

Influence of key cement chemical parameters on the properties of metakaolin blended cements

Abstract: The use of metakaolin (MK) as a mineral admixture for cement and concrete is a well-documented practice. The properties of cement pastes and mortars containing MK have been investigated as a function of key cement chemical parameters recognized as potential activators of the MK. Rheological behavior, initial setting time and compressive strength development have been compared by varying the total sulfate content, the nature of the added calcium sulfate and the free lime content (in the form of portlandite) in the cement. The results obtained indicate that it exists a compromise for the ratio performance/consistency in term of sulfate content and nature. Concurrently, a small addition of portlandite improves the consistency of the properties investigated.

About the analysis of microcracking in concrete

Abstract: This paper deals with the techniques of characterisation of cracks and microcracks in concrete and mortars. It gives an overall view of the methods of observation in relation with image analysis. Image analysis is a useful tool to extract crack patterns from samples of concrete, since many fields are necessary to be studied at high magnifications. An analysis of the procedures and of the provided 2-D data is proposed. The parameters of damage characterisation are listed and discussed. Improvements and ways of research are suggested, mainly to extend 2-D results to 3-D space by means of crack-pattern modelling.

Some fields of applications of automatic image analysis in civil engineering

Abstract: This paper illustrates the use of automatic image analysis technique to investigate the morphology of cement, concrete and fibre-reinforced concrete. First the methods to be used for powders and secondly for mortar and concrete are introduced. The dispersed phases are characterized by classical morphological parameters: these also enable to accede to the hydration process. The covariances give quantitative information on the homogeneity and dispersion of the different components: gravel, air-voids and cement paste. Air-voids are characterized by granulometric distributions and their mean free paths. Rose of directions gives information on feature orientation: fibres, microcracks for fibre-reinforced concrete, etc. Finally probabilistic models can be used to simulate the microstructure of such materials.

A design consideration for durability of high-performance concrete

Abstract: Environmental factors, especially the climate, have significant influence on concrete structure. This paper aims to investigate the harmful effects of maritime climate on the durability of concrete structures built in coastal areas. Singly reinforced beam specimens of traditional design and those of densified mixture design algorithm (DMDA) were employed to study the potential problems of concrete structure. Results indicate that cracks on the concrete structure, if go unnoticed, may cause failures. Thus, it is important to know the methodology of achieving high strength and durable concrete in order to avoid formation of cracks in the structural member.

Ground iron blast furnace slag as a matrix for cellulose-cement materials

Abstract: The use of ground iron blast furnace slag (BFS) as a low-cost alternative to ordinary Portland cement (OPC) binders in fibre-cement products was examined. Both high quality softwood fibres and residual sisal from agricultural waste were chemically pulped and used as reinforcement. Composites based on several different binder formulations consisting of slag chemically activated by mixtures of gypsum and hydrated lime displayed their optimum strength and fracture toughness properties at fibre contents between 8% and 12%, with values in the ranges of 14.7–24.5 MPa and 1.13–2.36 kJ/m2, respectively. Corresponding flexural moduli lay in the range 4.3–7.8 GPa and, at 12% fibre content, the composites possessed water absorption values up to 34% by mass and densities in the region of 1.3 g/cm3. A formulation of BFS activated by 10% gypsum and 2% lime presented a good compromise between strength and energy absorption combined with a reasonable price.

Resistance to biogenic sulphuric acid corrosion of polymer-modified mortars

Abstract: The use of polymer-modified mortar and concrete (PMM and PMC) is investigated to improve the durability of concrete sewer pipes. The aim of the research is to ameliorate the resistance of concrete to biogenic sulphuric acid attack through polymer modification. Prior to the durability tests, experimental research is carried out to reveal the influence of polymer modification on the physical and mechanical properties of mortar and concrete. The results of this research are presented in this paper. Due to the interaction of the cement hydrates and the polymer particles or film, an interpenetrating network originates in which the aggregates are embedded. The density, porosity and location of the polymer film depend on the type of polymer emulsion and on its minimum film-forming temperature (MFT). If air entrainment is restricted, an increased flexural strength is measured. Scanning electron microscope (SEM) analyses reveal the presence of polymer film and cement hydrates in the mortar. The polymer film causes a retardation of the cement hydration as well as a restriction of crystal growth.

Reconstructions by SPACE of the Interfacial Transition Zone

Abstract: Of particular interest in concrete technology is the so-called Interfacial Transition Zone (ITZ). Conflicting experimental evidences as to the internal structure and extent of the ITZ, and even as to the very existence of it, make it attractive to confront such observations with a coherent picture of the ITZ produced by computer-simulation, although based on a simplified model concept. This contribution outlines the scientific framework for interpretation of the so-called packing phenomenon. A dynamic computer-simulation system, Software Package for the Assessment of Compositional Evolution, with the acronym SPACE was recently developed by the second author, and has been used for the present purpose. In addition to properly simulating composition of particulate materials, as can also be achieved by conventional systems based on random sequential procedures, it has been demonstrated earlier that SPACE can also more accurately reproduce configuration of particles in such materials. An hydration algorithm is additionally implemented in SPACE. Some preliminary information on gradient structures in the ITZ are discussed. The extent of packing gradients in the fresh and hardened state will be shown to vary with changes in material composition (water to cement ratio, cement fineness) and in the configuration-sensitivity of the parameter being studied. This implies structural gradients to extend further away from aggregate grain surfaces the more sensitive the very parameter is to packing configuration. Particular emphasis is given to this fundamental aspect, and not to properly estimating the ITZ's thickness of this model cement paste near boundaries. Tools are provided to extract 2-D structural data from imaginary section planes (or from imaginary thin section projections) of the ITZ parallel to the interface. By making use of stereological methods, such data are given a 3-D structural meaning. Of course, direct information on porosity, packing characteristics and local particle distributions is available in 3-D. Therefore, in some cases direct 3-D measurements are possible, as well as visualisation of parts of the structure.

Some findings on the usefulness of image analysis for determining the characteristics of the air-void system on hardened concrete

Abstract: This paper discusses the usefulness of image analysis techniques in order to assess the characteristics of the air-void system in concrete. Test results indicate that such a technique can correctly assess the air-void characteristics as defined in ASTM C 457 Standard test method. However, the accuracy of the test results is not significantly improved as compared with the manual technique and the image analysis method must be very carefully validated before being used as a routine procedure. Test results also indicate that the image analysis technique failed to correctly assess the size-distribution of air voids and, for that reason, this technique cannot be used to provide a better estimate of the real spacing of air voids than the commonly used ASTM C 457 spacing factor.

Image analysis: a tool for the characterisation of hydration of cement in concrete – metrological aspects of magnification on measurement

Abstract: This study aims at seeking what magnification is optimal in view to evaluate the hydration state of cement-based materials. When observing surfaces of flat polished sections of cement paste and mortar under SEM in BSEI mode at 100x, 200x, 400x, 600x, 1000x magnifications, an image analysis procedure, derived from the entropy maximisation, is applied to evaluate the area fraction of the anhydrous remnant cement grains at a given maturity. Results show that: 200x is sufficient to correctly determine anhydrous remnant cement grains since higher magnifications induce marginal variations of anhydrous remnant cement grains; by calculating the covariance, 200x is also a representative field to describe the dispersion of the anhyrdous phase. The number of fields necessary to obtain a mean value of anhydrous remnant cement grains with a defined accuracy at 200x is specified according to statistical laws. (A)