Showing papers in "Cement & Concrete Composites in 1999"

Stress-strain curves for steel-fiber reinforced concrete under compression

Abstract: Steel-fiber reinforced concrete is increasingly being used day by day as a structural material. The complete stress–strain curve of the material in compression is needed for the analysis and design of structures. In this experimental investigation, an attempt has been made to generate the complete stress–strain curve experimentally for steel-fiber reinforced concrete for compressive strength ranging from 30 to 50 MPa. Round crimped fibers with three volume fractions of 0.5%, 0.75% and 1.0% (39, 59, and 78 kg/m3) and for two aspect ratios of 55 and 82 are considered. The effect of fiber addition to concrete on some of the major parameters namely peak stress, strain at peak stress, the toughness of concrete and the nature of the stress–strain curve is studied. A simple analytical model is proposed to generate both the ascending and descending portions of the stress–strain curve. There exists a good correlation between the experimental results and those calculated based on the analytical model. Equations are also proposed to quantify the effect of fiber on compressive strength, strain at peak stress and the toughness of concrete in terms of fiber reinforcing parameter.

Residual strength and pore structure of high-strength concrete and normal strength concrete after exposure to high temperatures

Abstract: Based on normal strength concrete (NSC) and high-strength concrete (HSC), with compressive strengths of 39, 76, and 94 MPa respectively, damage to concrete under high temperatures was identified. After exposure to temperatures up to 1200 °C, compressive strength and tensile splitting strength were determined. The pore structure in HSC and in NSC was also investigated. Results show that HSC lost its mechanical strength in a manner similar to that of NSC. The range between 400 and 800 °C was critical to the strength loss. High temperatures have a coarsening effect on the microstructure of both HSC and NSC. On the whole HSC and NSC suffered damage to almost the same degree, although HSC appeared to suffer a greater worsening of the permeability-related durability.

Influence of finely ground limestone on cement hydration

Abstract: Some work has been carried out on the effect of calcium carbonate on cement paste, but there is no general agreement on the relative effects of different amounts of calcium carbonate on cement paste properties. The objective of the present work is to assess the effect of various amounts of calcium carbonate on the hydration of tricalcium silicate in order to explain the physico-chemical changes occurring during Portland cement hydration. It is shown that calcium carbonate has an accelerating effect on C3S and cement hydration and leads to the precipitation of some calcium carbosilicate hydrate.

Behaviour of composite soil reinforced with natural fibres

Abstract: Next to the food shortage, the housing shortage is one of the most crucial problems on earth. To improve this situation and make it possible to build more houses, particularly for low-income families, it is necessary to examine all locally available materials which can be used for construction. Bamboo, sisal and coconut fibres are materials which are available in abundance in Brazil and are not used in civil construction. To increase the amount of information concerning the physical and mechanical behaviour of these materials several research programmes were executed at Pontifical Universidade Catolica in Rio de Janeiro (PUC-Rio) and Universidade Federal da Paraiba (UFPb) under the general supervision of the first author. In this paper new results are presented concerning the application of sisal and coconut fibres in conjunction with three types of locally appropriate soil for the production of composite soil blocks reinforced with sisal and coconut fibres.

Polymers in concrete: a vision for the 21st century

Abstract: Polymers in concrete have received considerable attention over the past 25 years. Polymer-impregnated concrete (PIC) was the first concrete polymer composite to receive widespread publicity. PIC has excellent strength and durability properties, but it has few commercial applications. Polymer concrete (PC) became well known in the 1970s and is used for repair, thin overlays for floors and bridges, and for precast components. Polymer-modified concrete (PMC) has been used primarily for repair and overlays. Several limitations have slowed the use of concrete polymer materials. However, there are many current and future uses for these materials that will effectively use their unique properties. Improved, automated repair methods, improvements in materials, replacements for metals, structural applications, and architectural components will prove to be popular uses of concrete-polymer materials.

Durability of portland blast-furnace slag cement concrete

Abstract: This paper summarizes the results of studies carried out at the Building Research Establishment in the UK, on the performance and long-term durability of concrete where ground glassy blast-furnace slag (granulated and pelletized) has been used as a cementitious material. Using data from tests on site structures and laboratory and exposure site studies, comparisons are made of the properties and performances of the slag cement concretes with normal Portland cement concretes of similar mixture proportions. A number of recommendations are given for the effective use of ground glassy blast-furnace slag in concrete. The many technical benefits available to the concrete user, such as reduced heat evolution, lower permeability and higher strength at later ages, decreased chloride ion penetration, increased resistance to sulfate attack and alkali silica reaction were affirmed. However, a cautionary warning of the importance of good early curing is made to ensure that the adverse effects of higher rates of carbonation, surface scaling and frost attack are minimized. The paper is intended to provide guidance for those concerned with the design, specification, application and performance of concrete in practice where slag can also help to reduce costs and energy demands in the production of cement compared with normal Portland cement.

Comparative study of the initial surface absorption and chloride diffusion of high performance zeolite, silica fume and PFA concretes

Abstract: Zeolite, a type of natural pozzolanic material, has been used in producing blended cement and concrete in China. The purpose of this study is to evaluate the effectiveness of zeolite in enhancing the performance of concrete in comparison with silica fume and pulverized fuel ash (PFA). In the first series of experiments, zeolite, silica fume, and PFA were all used to replace 5%, 10%, 15% and 30% of cement by weight in concrete with water to total cementitious material ratio (W/(C + P)) kept at 0.28. The results showed that zeolite decreased bleeding and increased marginally the viscosity of concrete without significantly compromising the slump. And at 15% replacement level, it resulted in 14% increase in concrete strength at 28-day compared with the control concrete. The test results also showed that there existed an optimum replacement level for zeolite to effect a decrease in initial surface absorption and in chloride diffusion of concrete. The test results of the second series of experiments where zeolite, silica fume and PFA were in turn used to replace 10% of cement in concretes with W/(C + P) in the range of 0.27 to 0.45 appeared that zeolite performed better than PFA but was inferior to silica fume in terms of increasing strength, decreasing initial surface absorption and chloride diffusion. It was further found that when W/(C + P) was greater than 0.45, the strength of the concretes incorporating zeolite or PFA (by direct replacement) was lower than that of the control concrete. The micro-structural study on concrete with zeolite revealed that the soluble SiO2 and Al2O3 could react with Ca(OH)2 to produce C–S–H which densified the concrete matrix. Pozzolanic effect of zeolite improved the microstructure of hardened cement paste and reduced the content of the harmful large pores, hence made concrete more impervious.

Thaumasite — background and nature in deterioration of cements, mortars and concretes

Abstract: Thaumasite has been shown to form at low temperatures, particularly 0–5 °C, as a non-binding calcium carbonate silicate sulphate hydrate under conditions of destructive sulphate attack. Formation of thaumasite arises generally from calcium silicate hydrate CSH and Ca2+, CO2−3, SO2−3, CO2 and water, or from ettringite in the presence of CSH, carbonate and/or carbon dioxide and water. It basically resembles a carbonated ettringite, with which it has often been confused in the past. Conversion of the main cementitious binder CSH into the non-binder thaumasite is a destructive form of sulphate attack. Greater awareness of the potential problems that thaumasite can cause has arisen with the increased use of limestone fillers in cements, the common employment of limestone aggregates in concrete and the introduction of Portland limestone cements, together with the realisation that structural foundations of buildings are, on average, below ambient temperature and (more often than not with on- and above-ground construction) are within the optimum temperature range for thaumasite to be formed. Instances have been found in specific studies of large quantities of thaumasite being formed in foundation concretes with no evidence for any structural damage above ground level. It is important to be aware of the propensity of thaumasite to form at low temperatures for mix designs, so as not to encourage any destructive sulphate attack by thaumasite to arise. This means utilising low water cement ratios for workable mortars and concretes, so as to give reduced permeability. This will prevent, or at least suitably hinder, ingress of destructive ions and water, so that the potential for destructive sulphate attack by formation of thaumasite is not actually realised in practice.

A study on the parameters affecting the properties of Portland limestone cements

Abstract: In this paper the parameters affecting the properties of Portland limestone cements are investigated. Portland limestone cements of different fineness and limestone content have been produced by intergrinding clinker, gypsum and limestone. Two kinds of clinker of different chemical composition, mineralogical composition and strength development and three limestones, with different contents of calcite, dolomite, quartz and clay, have been used. It is concluded that the appropriate choice of the clinker quality, limestone quality, % limestone content and cement fineness can lead to the production of a limestone cement with the desired properties. Limestone cements, having up to 10% limestone content and fineness up to a limit value, develop almost the same compressive strength, as the corresponding pure cements. The limestone cements, generally have lower paste water demand than the relative pure cements and the water demand decrease is mainly affected by the clinker type and limestone quality. In any case the properties of the limestone cements are affected by the interaction of the two components rather than their individual properties.

Transition zone studies of vegetable fibre-cement paste composites

Abstract: The transition zone of short filament fibres randomly dispersed in a paste of ordinary Portland cement was analysed. Composites with vegetable fibres (malva, sisal and coir) were compared with those with chrysotile asbestos and polypropylene fibres. The composites were prepared for testing at the ages of 7, 28, 90 and 180 days. The water-cement ratio was 0.38; at the age of 28 days specimens with w c = 0.30 and a w c = 0.46 were also tested. Mechanical tests evaluated the composite tensile strength and ductility. Backscattered electron imaging (BSEI) and energy dispersive spectroscopy (EDS) were used to identify the major properties of the fibre-matrix interface. Mainly for vegetable fibre composites the transition zone is porous, cracked and rich in calcium hydroxide macrocrystals. These characteristics are directly related to the fibre-matrix bonding and to the composite mechanical performance.

Durability of reactive powder composites: influence of silica fume on the leaching properties of very low water/binder pastes

Abstract: Reactive Powder Composites are new cement-based materials which could be used for the storage of nuclear wastes thanks to their excellent microstructural properties. This paper studies their durability when submitted in the laboratory to a water leaching attack. In order to understand the behaviour of the hydrates (CSH), the study was carried out on a pure cement paste and on a cement + silica fume paste. The beneficial effect of silica fume is demonstrated from considerations on the calcium leaching, from XRD analysis, from SEM observations and from the tritium diffusion and pore distribution analysis. It was found that the leaching greatly affects the microstructure, especially that of the anhydrous cement grains remaining in the paste.

Modelling the loss of strength and porosity increase due to the leaching of cement pastes

Abstract: Pure water leads to a progressive decalcification of hardened cement pastes. The physical and chemical processes of this degradation are relatively well defined today, but the consequences of the leaching on the porosity increase and the loss of strength have been only partially studied. Our work consists of correlating the alteration of these properties with the rate of degradation of the material. The leaching is achieved by an accelerated process. Compressive strength and water porosity are measured after different processing times in an aggressive solution. A physical phenomenon analysis leads us to propose a stress distribution model at rupture, and a calculation model of the porosity increase, taking into account the nature of the degraded hydrates (CSH).

Influence of the proportion of wood on the thermal and mechanical performances of clay-cement-wood composites

Abstract: The introduction of wood aggregates to produce low density composites is an interesting technique allowing the reuse of wastes from both the aggregate-mining and wood processing industries. This paper describes the influence that the proportion of wood aggregates has on the thermal and mechanical performance of a clay-cement-wood composite. First, the composite material and its production technique are presented. Then, the thermal conductivity, mechanical strengths and the porosity of the matrix are experimentally evaluated. Finally, it is shown that the addition of wood to clayey concrete improves its insulation characteristics, reduces its mechanical strength and increases its deformability.

Resistance of fibre concrete slabs to low velocity projectile impact

Abstract: An investigation on fibre concrete slabs subjected to low velocity projectile impact was carried out to assess impact resistance. The main variables of the study were type of fibre and volume fraction of fibres. The types of fibres chosen were polyolefin, polyvinyl alcohol and steel. The volume fraction of fibres examined were 0%, 1% and 2%. A total of 10 square slabs of size 1 m and 50 mm thickness were cast and tested. Impact was achieved by dropping projectile of mass 43 kg from a height of 4 m, by means of an instrumented impact test facility. Test results indicate that hooked-end steel fibre concrete slabs have better cracking and energy absorption characteristics than slabs reinforced with other fibre types. Slabs reinforced with polyvinyl alcohol fibres exhibited higher fracture energy values compared to slabs reinforced with polyolefin fibres.

Aging mechanisms in cellulose fiber reinforced cement composites

Abstract: This paper examines the effects of laboratory scale accelerated aging exposures on the changes in physical and mechanical properties of commercially produced cellulose fiber reinforced cement composites. Two different accelerated aging methods were used to simulate the possible aging mechanisms for which the material may experience under service conditions, both methods being compared to material naturally weathered for 5 yr in roofing. The first aging method consisted of different cycles of water immersion, carbonation, and heating exposures whereas in the second method, cycles of water immersion, heating and freeze-thaw exposures were used. The porosity, water absorption, permeability of nitrogen and compressive shear strength of the composites were examined before and after aging exposures. The surface morphologies of the composites fractured in compression shear tests were examined using scanning electron microscope. Experimental results showed that the compressive shear strength of the accelerated aged composites were related to the microstructures within the composites. Both natural weathering and accelerated aging in CO2 environment reduced the porosity, water absorption, and nitrogen permeability in the cement matrix, and enhanced the durability of the cellulose fiber-cement composites. The aging test based on artificial carbonation was more effective in simulating natural aging performance of the composites, while the freeze-thaw cycling method failed to induce significant aging effects on the composites even after 21 cycles.

Thaumasite formation and deterioration in historic buildings

Abstract: Thaumasite and ettringite can be found among the deterioration products of cementitious materials exposed to sulphate attack. This can occur in concrete structures, as well as in masonry walls of historic buildings erected before the advent of Portland cement. Masonry walls of historic buildings may contain gypsum or other sulphate salts for different reasons. When they need to be repaired, CSH and CAH, formed by the hydration of hydraulic binders used for restoration, can react with water and gypsum or sulphate salts and produce thaumasite and ettringite. Due to these reactions, degradations of the repaired historic buildings can occur causing expansion, cracking, spalling and strength loss. In order to assess preliminarily the chemical compatibility of a repairing cementitious material with the presence of gypsum or sulphate salts inside historic buildings, the Anstett test can be adopted. Alternatively, protection measurements, based on the hindrance of water to penetrate the walls, should be adopted since in the absence of water both thaumasite and ettringite cannot be produced, even in the presence of gypsum, or other sulphate salts inside the historic buildings.

Properties of high-strength steel fiber-reinforced concrete beams in bending

Abstract: This paper presents research results of ten high-strength reinforced concrete beams and steel fiber-reinforced high strength concrete beams, with steel fiber content of 1% by volume. The enlarged ends of mild carbon steel fibers with three different dimensions were selected. This research shows that the flexural rigidity before yield stage and the displacement at 80% ultimate load in the descending curve are improved, and crack number and length at comparable loads is reduced after the addition of steel fibers. The descending part of the load-displacement curve of the concrete beams without steel fibers is much steeper than that with steel fibers, which shows that the addition of steel fibers makes the high strength concrete beams more ductile.

Lightweight concrete in hot coastal areas

Abstract: An experimental study was carried out to examine different mixtures made with selected lightweight aggregates for the purpose of producing lightweight concrete. A relatively suitable product is sought in order to provide good quality building materials that can satisfy the conditions of hot coastal environments. Three ways of producing lightweight concrete were used, i.e., lightweight crushed bricks, lightweight expanded clay aggregate (LECA), and no-fines concrete. Physical and mechanical properties of the mixtures were examined to ascertain the suitability and applicability of the three concretes. The results of this pilot study suggest that there are possibilities of producing structural lightweight concrete using crushed bricks with the condition of further refinements in the mixture design.

Micromechanical modeling of crack-aggregate interaction in concrete materials

Abstract: A new condition for crack penetration into the aggregate phase in concrete materials is developed based on numerical simulations. The numerical simulation utilizes a newly developed micromechanical model which considers the concrete internal structure as a three-phase material, viz. matrix, aggregate and interfaces between them. The micromechanical model is capable of capturing the entire load-deformation response of a concrete specimen under monotonic loading including softening. The new condition for crack penetration is developed based on a simple specimen configuration where a crack is driven towards an aggregate particle. Results from numerical simulations are implemented to relate the relative properties of both aggregate and matrix phases (represented by the characteristic length ratio) to their tensile strength ratio. It is shown that the tensile strength ratio between the aggregate and the matrix plays the dominant role in determining the penetration condition. Predictions based on this condition agree with direct tensile simulations using different specimen configuration.

Fiber/cement interface tailoring with plasma treatment

Abstract: A comprehensive study on the optimal conditions of plasma treatment of polyethylene fibers on their interfacial property with cement matrix is reported in this paper. Single fiber pullout tests were performed for bond property evaluation. With the optimal treatment conditions, a sixfold increase in bond strength or sevenfold increase in interfacial toughness can be achieved separately. Furthermore, a distinct interfacial chemical bond, compared to common frictional bond was observed for the first time in the polyethylene/cement systems. On the matrix side, matrix modifiers such as high alumina cement and PVA powder were also studied to examine their additional influence on the interface properties. Some preliminary results of the stability of plasma treatment are also reported in this paper.

Influence of superplasticizer and curing on porosity and pore structure of cement paste

Abstract: Most concrete produced today contains admixtures. Superplasticizers (SP) are used for the purpose of improving workability and reducing the water to cement ratio; therefore producing more durable concrete. SP cause better dispersion even at high water to cement ratio. Although SP improves the dispersion of particles, it is not quite clear how the addition of SP affect the porosity and pore size distribution of cement paste. The purpose of this study was ro examine the influence of one type of SP on porosity and pore size distribution under different curing regimes. Paste specimens with and without SP were prepared at constant water to cement ratio of 0.45. Specimens were cured for 28 days and some for six months. Specimens were exposed to high temperature (45 degrees C) and normal temperature curing (20 degrees C) and also subjected to different relative humidities (similar to 100%, 55% and 25%). Curing at high temperature was carried out to simulate temperature in hot climates. Tests on porosity and pore size distribution were conducted using mercury intrusion porosimetry. The results show that the inclusion of SP decreases the total intruded pore volume of paste. The dominant pore diameter, however, does not seem to be affected and the percentage of pores smaller than 100 nm increases in the presence of SP. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.

Effect of addition time of a superplasticizer on cement adsorption and on concrete workability

Abstract: The effect of addition time of a naphthalene-based superplasticizer (SNF) on the adsorption behavior on type I Portland cement slurries and on the concrete workability was studied. Test results indicate that the adsorption behavior of SNF on cement particles follows a Langmuir isothermal adsorption model. As the addition time increases, the saturated adsorption amount of SNF decreases sharply at the beginning and then more slowly. In comparison, the concrete workability decreases slightly in the early phase and then falls off abruptly. Most importantly, the transition points in both cases appear to be the same, at about 10–15 min. This strongly suggests that a close relationship exists between the SNF adsorption behavior on cement particles and the workability of concrete. In addition, the optimum addition time of SNF to concrete should be in this period, which corresponds to the beginning of the dormant period of the cement hydration process.

The effect of clinker and limestone quality on the gas permeability, water absorption and pore structure of limestone cement concrete

Abstract: In this paper the effect of clinker and limestone quality on the air permeability, water absorption and pore structure of limestone cement concrete is investigated. Portland limestone cements of different fineness and limestone content have been produced by intergrinding clinker, gypsum and limestone. Two clinkers with different chemical composition, mineralogical composition and strength development as well as three limestones, differing by their calcite, dolomite, quartz and clay contents, have been used. It is shown that the clinker quality significantly affects the gas permeability and sorptivity of the limestone cement concrete. Limestone cements with high C3A and alkalis content seem to be more appropriate for improving the permeability properties of concrete. In addition, the effect of the limestone quality on the concrete permeability is not well established. The pore size distribution and more specifically the mean pore size affects the gas permeability and the sorptivity of the concrete. Finally it is concluded that, depending on the clinker quality and the cement fineness, limestone cement concrete, with an optimum limestone content, can give lower gas permeability and water absorption rate as compared with pure cement concrete.

Fatigue life analysis of fiber reinforced concrete with a fracture mechanics based model

Abstract: Fatigue life of fiber reinforced concrete (FRC) is theoretically analyzed with a fracture mechanics based model. The model accounts for the effect of cycle-dependent crack bridging properties in FRCs and predicts the number of cycles to failure defined by final fracture subsequent to stable fatigue crack growth in Mode I. The resulting theoretical S–N diagram was compared with experimental data reported in literature. The general agreement supports the validity of the current model, and reveals that cycle-dependent degradation of crack bridging controls fatigue life of FRCs. S–N diagrams are essential for material evaluation and structural design, and the model establishes the link between material structure and S–N diagram in an explicit manner, while the conventional stress-life approach realizes the link in an empirical manner.

Influence of aggregate fraction in the mix on the reliability of the rapid chloride permeability test

Abstract: The present paper elucidates the influence of aggregate content of the mix on the reliability of rapid chloride permeability test (RCPT) results. For this purpose, test specimens prepared with mixes varying in total aggregate content were subjected to soaking test, RCPT and electrical resistivity measurements, and the results from these tests were compared and conclusions drawn. The RCPT results indicated the plain cement concrete to be relatively more resistant against chloride penetration than the plain cement mortar, whilst the opposite was true according to the 90-day soaking test results. The above trend did not change despite the addition of silica fume (SF) to the concrete and mortar mixes. The lower aggregate content or higher paste content of plain cement mortar and the mortar with SF is shown to mislead the RCPT results. The higher paste content in the above mix promotes the conduction of higher charge as a result of lower electrical resistivity. Thus the results derived from the present investigation emphasize the need to consider the volume fraction of aggregate in the mix with and without SF while interpreting the RCPT results. Furthermore, regardless of the total aggregate and SF content in the mix, the total charge passed (from the RCPT) through the mix decreased exponentially with increasing electrical resistivity. On the other hand, for those mixes containing either SF or a high volume fraction of aggregates the linear correlation between the total charge passed and chloride penetration coefficient (K) was poor. However, for the mix with relatively lower aggregate content and with no SF the charge passed was well correlated linearly with K.

Flow behaviour of high strength high-performance concrete

Abstract: The workability of flowable High-Performance Concrete (HPC) is nowadays mainly measured using conventional test methods such as the slump test or the slump-flow test. These single-point tests do not seem sensitive enough to characterize the high-workability of HPC. Due to the fluid consistency and uniformity of fresh HPC, it is possible to describe its flow properties by using a rheological test method. To evaluate the flowability based on rheology, fresh HPC is regarded as a two-phase material composed of a matrix phase and a particle phase. In the study, the effects of materials and proportioning on the rheological properties were investigated experimentally. A new rheometer was established by conducting a two-point test to investigate the flow behaviour of high strength HPC. Test results show that the high strength HPC with good uniformity and without tendency of segregation can possess the properties of rheology according to Bingham’s equation. An increase of the fraction of mortar in HPC can lead to a more distinct the rheological behaviour. Moreover, it is found that the application of a rheological method can provide more stable results than any other test method in describing the flowability of high strength HPC.

Mechanical behaviour of ferrocement composites: an experimental investigation

Abstract: In-plane tension, compression and bending tests were conducted on plain mortar and ferrocement specimens with woven and welded meshes. Tension tests were also carried out on meshes. Bending tests were conducted using specimens with centre point loading. The objective of the study was to investigate the behaviour of material reinforced with varying number of mesh layers and orientations and to evolve a set of elastic and inelastic material properties. It is observed that the conventional empirical relations based on mortar crushing strength overestimate the mortar modulus. The elastic moduli obtained using the rule of mixtures compares well with the values evaluated from the tests on ferrocement specimens. The 45° orientation emerges as the weakest configuration both in terms of the Young's modulus and ultimate stress because of the lowest volume fraction of wire mesh in the direction of loading at this orientation.

Performance of Portland limestone cements in mortar prisms immersed in sulfate solutions at 5 °C

Abstract: The results of a test programme to investigate the sulfate resistance of mortars, immersed up to 12 months at 5 °C in magnesium sulfate and sodium sulfate solutions, is described. The mortars were prepared from four cements; a Portland cement, a sulfate-resisting Portland cement and two Portland limestone cements containing 15% by mass of an oolitic limestone and a carboniferous limestone. The mortar specimens were subject to BS 5328 Class 4A and 4B sulfate exposure conditions. These are the highest classes for concretes prepared using sulfate-resisting Portland cement (SRPC) before surface protection is required and are two and three classes higher than those recommended for concretes prepared using Portland cement (PC) and Portland limestone cement (PLC), respectively. Two free water-cement ratios were used, 0.5 and 0.75. Performance was monitored by visual assessment, expansion and changes in flexural and compressive strengths. At a free water-cement ratio of 0.75, the PC mortars and PLC mortars exhibited visually very severe attack with the former showing expansion and reductions in strength, and the latter mainly reductions in strength. At a free water-cement ratio of 0.50 both the PC mortars and PLC mortars showed slight/moderate to severe visual attack, the degree of deterioration appearing slightly greater in the PLC mortars, more especially those made with oolitic limestone. The PLC mortars also exhibited reductions in compressive failure load. The SRPC mortars exhibited little visual deterioration, no expansion, a small increase in flexural strength and no significant reductions in compressive strength. At a free water-cement ratio of 0.75 substantial amounts of thaumasite, together with ettringite was present in the surface layers of the deteriorated PLC mortars whilst ettringite was present in the surface layers of the deteriorated PC mortars. It is concluded that mortars made with a PC with a C 3 A content of about 10% by mass were broadly similar in their vulnerability to sulfate attack at 5 °C as PLC mortars containing 15% limestone by mass, although the mode of attack was different.

Limestone aggregate concrete, usefulness and durability

Abstract: Inland and on sea coasts, crushed limestone aggregate has been used in France and elsewhere for structural concrete when gravel aggregates were not available. Crushed limestone fillers have, since the oil crisis, been allowed as partial constituent of cement; they are now currently used as additions in concrete mixtures, as partial replacement of Portland cement. Limestone aggregate concretes have not been considered inferior to gravel aggregate concretes, particularly in durability. However, recently some cases of alkali-silica deleterious reactivity and one case of sulphate attack, have questioned their good performance status.