Showing papers on "Mortar published 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.

Remediation of Concrete Using Micro-Organisms

Abstract: This paper describes an innovative biotechnology-utilizing, microbiologically-induced mineral precipitation for concrete remediation. Calcite precipitation induced by Bacillus pasteurii was studied in 2 types of portland cement mortar (PCM) specimens: 1 prepared from mixing with micro-organisms, and the other with simulated cracks filled with microbial mixtures. Study results show that there was a significant increase in compressive strength of the PCM cubes containing lower concentrations of live cels. Compressive strengths of the cubes containing live or dead cell mass, however, decreased as cell concentrations and curing time increased, suggesting the interference of mortar integrity by biomass. Cracks filled with bacteria and sand demonstrated a significant increase in compressive strength and stiffness values when compared with those without cells.

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.

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.

Pore water distribution in mortar during drying as determined by NMR

Abstract: The drying of a saturated mortar sample was measured using Nuclear Magnetic Resonance. NMR is a technique which gives the total moisture content of a specific volume at a certain time. By looking also at the relaxation of behaviour of the NMR signal, more information can be obtained. For every time and every position, the pore size distribution of the mortar was measured. Other techniques show that NMR is a reliable method to measure pore size distributions. Two distinctive pore sizes can be seen in the pore size distribution. This corresponds to the microstructure of mortar, which has small (< 10nm) gel pores and bigger) ≈ 10 to 1000 nm) capillary pores. A one-dimensional drying experiment was carried out by blowing dry air (relative humidity =0+5%; temperature=20±1°C) ove the top of a cylindrical mortar sample, while all the other surfaces were sealed to prevent drying in other directions. The changing moisture content in the pores was followed with time during drying for about 3 days. This leads to the conclusion that the water cannot be extracted from the gel pores, while the capillary pores dry within about 20 hours under the drying conditions and time adopted.

Experimental analysis of compaction of concrete and mortar

Abstract: Compaction of concrete is physically a collapse of the material porous microstructure. It produces plastic strains in the material and, at the same time, an increase of its bulk modulus. This paper presents two experimental techniques aimed at obtaining the hydrostatic response of concrete and mortar. The first one is a uniaxial confined compression test which is quite simple to implement and allows to reach hydrostatic pressures of about 600 MPa. The specimen size is large enough so that concrete with aggregate sizes up to 16 nam can be tested. The second one is a true hydrostatic test performed on smaller (mortar) specimens. Test results show that the hydrostatic response of the material is elasto-plastic with a stiffening effect on both the tangent and unloading bulk moduli. The magnitude of the irreversible volumetric strains depends on the initial porosity of the material. This porosity can be related in a first approximation to the water/cement ratio. A comparison of the hydrostatic responses obtained from the two testing techniques on the same material show that the hydrostatic response of cementitious materials cannot be uncoupled from the deviatoric response, as opposed to the standard assumption in constitutive relations for metal alloys. This feature should be taken into account in the development of constitutive relations for concrete subjected to high confinement pressures which are needed in the modelling of impact problems.

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.

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.

An experimental study on the guidelines for using higher contents of aggregate microfines in portland cement concrete

Abstract: The use of manufactured fine aggregate (MFA) in portland cement concrete becomes more common as sources of natural sands are depleted. There is a great need to utilize MFA better, particularly the minus 85 micro m sizes. The development of specifications that aid aggregates producers, engineers, and specifying agencies in the utilization of MFA is of interest to many parties. Better utilization of crushed aggregates has both economic and environmental benefits for the construction and materials industry. This report presents some of the effects of high-fines on the properties of cement mortar and concrete. A total of 5 sands were used in this mortar study, 10 of which were included in the concrete research. A summary of aggregate characteristics that affect the properties of mortar and concrete are presented along with the correlations evaluated between these properties.

Mechanical characterization of a styrene–butadiene modified mortar

Abstract: Polymer-modified mortars (PMCs) are used in the construction industry as tile adhesives or frontage coatings. This way of modifying classical mortars improves practical use and adhesion properties. However, the influence of the polymer phase on the durability and the mechanical properties of the modified mortars are still unknown. Three-point bending and compression tests were carried out on PMCs and classical mortar beams. The tests were made under strain control in order to reach the softening part of the stress–strain curve. The compression tests show the influence of polymer content on elastic characteristics, mechanical resistance and strain at rupture. Three-point bending tests reveal the PMC behavior in tension and the damage evolution is monitored by the loss of stiffness. Finally, scanning electron microscopy shows the polymer distribution in the composites.

NDE ultrasonic methods to characterise the porosity of mortar

Abstract: Premature damage of mortar and concrete structures, due to environmental action, demands procedures to estimate durability of this type of components Mortar or concrete composition (eg grain size, type and percentage of sand) may have some influence in the durability, but it is mainly related to porosity, which determines the interaction between aggressive agents and material In this work, several IDE ultrasonic methods to estimate porosity of mortar are presented and evaluated In these methods, porosity is related to (1) the material structural noise, (2) sound velocity and (3) ultrasonic attenuation In all these methods, mortar is consider to be formed by only two phases: solid and pores

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.

Use of electrodeposition for repair of concrete with shrinkage cracks

Abstract: The electrodeposition method for repair of cracked reinforced concrete is presented here. Electrodeposition means precipitation of material on the surface of an electrode by electrolysis. The ultimate purpose of this study is to apply this technique to land-based reinforced concrete structures. Investigations on mortar specimens with embedded steel were conducted. After cracking the specimens with a specified load, they were immersed in several types of solutions. Then a constant current between the embedded steel in mortar and an electrode in the solution was applied. The deposition pattern on the surface, the crack closure development, and surface coating due to the precipitation of electrodeposits were checked and evaluated. In order to assess the effectiveness of this method to improve the mortar surface, water permeability, pore size distribution, and adhesion strength were measured. The results indicate that electrodeposits formed on the mortar surface are able to close the crack and coat the mortar surface. In addition, the investigations show that the deposition product can improve the microstructure of the mortar surface.

An Improvement In Preparation Of Mortar For Radiocarbon Dating

Abstract: An error source in radiocarbon dating of ancient mortar is dead carbon of limestone mixed in the matrix. To eliminate the influence of limestone the difference in feasibility to react with acid between mortar and limestone is used. Since the rate of reaction depends on grain size use of a well-defined grain size can give a better separation between mortar and limestone. We present results for the grain size dependence of reaction rates for several mortar and limestone samples and discuss the application for dating.

Investigations of Sulfuric Acid Corrosion of Concrete. I: Modeling and Chemical Observations

Abstract: Degradation of a mortar specimen exposed to an acid sulfate solution was studied. The pH of the solution was maintained in the range of 4–5 for 8 days and 2–3 for 73 days. Data from the experiment were used to investigate the efficacy of a diffusion-reaction based model with a moving boundary for the corrosion process. Acid neutralization rates in the solution were used to calculate the corrosion rate constant for the mortar sample and to determine the effective diffusion rate of sulfuric acid in the corrosion layer. Visual observation of the cross section of the sample at the end of the experiment indicated that 0.82 mm was corroded. The data established the validity of the moving boundary paradigm for sulfide corrosion of concrete when the effective diffusion rate was a decreasing function of the age of the corrosion product being formed.

The effect of gamma radiation on the strength of Portland cement mortars

Abstract: This paper describes part of a research effort that investigates the influence of dose rate on the compressive strengths of Portland cement based materials These include Portland I, Portland V, and Portland V wit silica fume (SP)