Showing papers on "Mortar published in 1996"

The use of limestone in portland cement: a state-of-the-art review

Abstract: Data from published literature and laboratory tests regarding limestone additions to portland cement are reviewed. Emphasis is placed on additions of 5% or less. The effects of interground and blended limestone on the particle size distribution of cement and workability of mortar and concrete are reported. Hydration behavior is examined with regard to chemistry, heat evolution, microstructure, and setting time. The properties of hardened mortar and concrete made with limestone portland cement are examined and compared to those made with non-limestone portland cements - including compressive and flexural strength, volume stability, durability (permeability, carbonation, freeze/thaw resistance, sulfate and chloride resistance, and alkali-silica reaction), and interactions with mineral and chemical admixtures. Quality control of the limestone, limestone portland cement, and concrete is also discussed. In general, the addition of up to 5% limestone does not affect the performance of portland cement. Strengths of cements with limestone can be optimized by grinding to an appropriate particle size distribution. An optimized portland cement containing up to 5% limestone can exhibit improvements in workability as compared to the same cement without limestone. Energy requirements for both pyroprocessing and comminution are reduced by the addition of limestone.

A comparative study of concretes reinforced with carbon, polyethylene, and steel fibers and their improvement by latex addition

Abstract: Mortars containing carbon, polyethylene, and stainless steel fibers at the same volume fraction and with similar fiber diameters were compared in terms of tensile, compressive, and flexural properties. Carbon fibers, though having the lowest tensile modulus, strength, and elongation at break among the fiber types, gave mortar of the highest tensile strength and lowest cost; polyethylene fibers, due to their high ductility, gave mortar of the highest flexural toughness; and steel fibers gave mortar of the highest flexural strength. The tensile, compressive, and flexural strengths and flexural toughness were all increased by latex addition for any fiber type.

Toughening in cement based composites. Part I: Cement, mortar, and concrete

Abstract: This paper reviews the mechanisms of toughening in unreinforced cementitious materials, including cement paste, mortar, and concrete. The paper emphasizes the microstructural aspects of the different fracture processes that can potentially take place in these materials, and point out any possible interactions between these processes. Reference is made to three types of fracture process — frontal, crack tip and wake processes, and estimates of contributions to composite toughness of the individual mechanisms are included. It is shown that the fracture mode of a cementitious material closely relates to the types of fracture process that occur in that material. Based on the understanding of the conditions under which certain toughening mechanisms can take place in a given material, it may be possible to control the material fracture mode by tailoring the material microstructure.

Polymer-Modified Mortars and Concretes

Abstract: Publisher Summary Polymer-modified mortar and concrete are prepared by mixing either a polymer or monomer in a dispersed, powdery or liquid form with fresh cement mortar and concrete mixtures, and subsequently cured, and if necessary, the monomer contained in the mortar or concrete is polymerized in-situ. Several types of the polymer-modified mortars and concretes— namely, latex-redispersible polymer powder-, water-soluble polymer-, liquid resinand monomer-modified mortars and concretes are produced by using the polymers and monomer. Of these the latex-modified mortar and concrete are by far the most widely used cement modifiers. Although polymers and monomers in any form such as latexes, water soluble polymers, liquid resins, and monomers are used in mortar and concrete, it is very important that both cement hydration and polymer phase formation proceed well to yield a monolithic matrix phase, with a network structure in which the hydrated cement phase and polymer phase interpenetrate into each other. In the polymer-modified mortar and concrete structures, aggregates are bound by such a co-matrix phase. The superior properties of the polymer-modified mortar and concrete to conventional mortar and concrete are characterized by such a distinct structure.

Flexural bond strength of masonry using various blocks and mortars

Abstract: This paper deals with an experimental study on flexural bond strength of masonry using various blocks in combination with different mortars. Flexural bond strength of masonry has been determined by testing stack-bonded prisms using a modified bond wrench test set-up. The effect of mortar composition and strength on the masonry's. flexural bond strength using three types of masonry units (stabilized mud blocks, stabilized soil-sand blocks and burnt brick) has been examined. The effect of the masonry unit's moisture content on flexural bond strength has also been studied. Increases in mortar strength lead to increased flexural bond strength for cement mortar, irrespective of the type of masonry unit. It has been found that combination mortars, such as soil-cement mortar and cement-lime mortar, lead to better bond strength compared to cement mortars. The moisture content of the masonry unit at the time of casting has displayed significant influence on the flexural bond strength of the masonry. It has been found that for each type of masonry unit, an optimum moisture content exists, beyond which the flexural bond strength falls off quickly.

Method for producing an ornamental concrete surface

Abstract: An ornamental coating and process for applying the coating to a substrate includes mixing a first batch of liquid mortar composed of sand, cement and an aqueous solution of acrylic resin, and trowelling or spraying a first layer of the liquid mortar onto the substrate and allowing the liquid mortar to cure. A second batch of liquid mortar is mixed which is the same as the first except that it contains a color pigment contrasting with the color of the first batch. A template defining a pattern of grout lines is placed over the cured first batch and the second batch of liquid mortar is trowelled or sprayed over the first batch and the template as a second layer and allowed to cure only to the extent that the second layer is firm, but not hard. The template is then removed, removing any part of the second layer immediately above the template thus exposing lines of the cured first batch which then appear as grout lines between areas of colored mortar which appear as bricks, flagstone or tiles etc. When the second batch has completely cured, two layers of concrete sealer are applied. The same coating may be applied over a properly supported wood substrate with proper preparation. An expanded galvanized metal lath is secured to the wood. This is then covered with a cementitious base coat which is allowed to substantially cure. The described ornamental coating then is applied over the base coat.

Fly ash cementitious material and method of making a product

Abstract: Rapid curing, high strength cementitious binder mixtures are provided containing fly ash and an alkali silicate binder that has a weight ratio of SiO2:M2O of about 0.20:1 to about 0.75:1 wherein M is selected from the group consisting of Li, Na, K, Ca and Mg. The cementitious binder mixtures can be mixed with aggregates to provide mortar and concrete mixtures. Any of the binder, mortar and concrete mixtures can be cured under elevated temperatures to yield high strenght products.

Method for increasing the rate of compressive strength gain in hardenable mixtures containing fly ash

Abstract: The present invention relates to concrete, mortar and other hardenable mixtures comprising cement and fly ash for use in construction. The invention provides a method for increasing the rate of strength gain of a hardenable mixture containing fly ash by exposing the fly ash to an aqueous slurry of calcium oxide (lime) prior to its incorporation into the hardenable mixture. The invention further relates to such hardenable mixtures, e.g., concrete and mortar, that contain fly ash prereacted with calcium oxide. In particular, the fly ash is added to a slurry of calcium oxide in water, prior to incorporating the fly ash in a hardenable mixture. The hardenable mixture may be concrete or mortar. In a specific embodiment, mortar containing fly ash treated by exposure to an aqueous lime slurry are prepared and tested for compressive strength at early time points.

A unilateral damage model for masonry based on a homogenisation procedure

Abstract: By considering masonry as a composite material, its mechanical properties are obtained by taking into account the properties of the components (bricks and mortar) through a homogenisation technique. To describe the behaviour of the material components a unilateral damage model is proposed. This model, based on the introduction of three damage variables, describes the behaviour of brittle materials subjected to alternating tensile–compressive cyclic loads. The model is applied to the simulation of tests on masonry panels and miniaturised walls; numerical results are discussed and successfully compared with experimental data.

Effects of curing conditions and age on chloride permeability of fly ash mortar

Abstract: Effects of fly ash type and content on the permeability characteristics of mortar materials subjected to two different curing conditions and two ages of testing were studied. Three different fly ash contents and three different fly ash types were examined in order to provide sufficient data for statistical analysis of results. Fly ash was observed to be capable of reducing the permeability of mortar, except for the Class C fly ash at lower cement substitution levels. Selection of fly ash type, the level of cement substitution with fly ash, curing conditions, and age of testing had important effects on the permeability characteristics of fly ash mortar; the interactions between these factors were also generally important. Results showed that as the moist-curing duration increased the fly ash mortar became less permeable. The interruption of moist-curing and exposure to a low-humidity environment led to increased permeability, except for the Class F fly ashes after longer moist-curing durations, for which permeability stayed almost constant. One may attribute this effect of air-drying to the formation of shrinkage microcracks, with particularly adverse effects on permeability that more than compensate for any positive effects of the slow progress of hydration or pozzolanic reaction in an environment with low humidity. In conclusion, assessment of mortar permeability based on a 28-day testing age after an initial moist-curing can be misleading.

Method and system for reclaiming aggregate from concrete waste material

Abstract: A method and system for reclaiming aggregate from concrete waste material includes crushing step and means of compression-crushing lumps of concrete waste material into a crushed mixture, and sorting the crushed mixture by size thereof, grinding step and means of rotating the crushed mixture sorted to grind it with a grinding member which rotates in an opposite direction to the rotating direction of the crushed mixture sorted, thereby peeling mortar from gravel, crushed stones and sand of the crushed mixture to obtain a mixture of gravel, crushed stones, sand, cement and mortar, and product separating step and means of separating the mixture of gravel, crushed stones, sand, cement and mortar into gravel and crushed stones, sand, cement and mortar.

Water quality deterioration from corrosion of cement–mortar linings

Abstract: Corrosion of cement-mortar lining-i.e., the leaching of lime from the cement matrix-can impair water quality by increasing pH, calcium, and alkalinity. Field tests at two utility sites evaluated the effects of water flow, lining method, seal coating, water quality, and cement-mortar composition. Water that remained stagnant in newly lined pipe sections for a relatively long time (one week) exhibited significant water quality effects-e.g., pH increases up to 12. Asphaltic seal coats significantly reduced cement-mortar corrosion in both tests. At one site, corrosion increased when the mortar contained Type II cement, a water- reducing admixture, pozzolanic material, or a high proportion of sand. At the other site, none of these parameters significantly affected results. Design and operating measures to minimize stagnation can reduce corrosion effects.

Investigation of stone matrix asphalt mortars

Abstract: The use of stone matrix asphalt (SMA) has continued to increase in the United States since its initial application in 1991. This preference for SMA has been linked to its ability to withstand heavy traffic without rutting. The antirutting capability of SMA is normally accredited to the presence of a stone-on-stone aggregate skeleton in the mixture. However, the mortar in an SMA mixture is also important. The mortar is composed of fine aggregate, filler, asphalt cement, and a stabilizing additive. Work to characterize SMA mortars is detailed. For testing purposes, the mortar was broken into separate phases, total mortar and fine mortar. The fine mortar was tested using the Superior Performing Asphalt Pavements system (Superpave) binder tests. The total mortar was tested using the bending beam rheometer, resilient modulus, indirect tensile test, and Brookfield viscometer. The results indicate that the fine and total mortars are closely related. In addition, it was determined that at least some of the Superpave tests can be used to characterize SMA mortars. It is recommended that further testing be completed and specification criteria be established for the mortar.

Factors influencing compressive strength of concrete masonry prisms

Abstract: This paper presents the results of an experimental investigation on blockwork masonry prisms to study the effect on their compressive strength and behaviour of the following factors: (a) concrete infill and mortar strengths; (b) specimen height-to-thickness ratio; (c) specimen length-to-thickness ratio; (d) mortar joint thickness; (e) bond between the block and concrete infill.

Tensile and compressive strength of silica fume-cement pastes and mortars

Abstract: The effect of silica fume on the compressive and uniaxial direct tensile strength of portland cement paste and mortar is reported. Sixteen and 25% of the cement used in the paste and in the mortar, measured by mass, was replaced by silica fume. Four different W/C ratio mixtures were tested: 0.22, 0.25, 0.28, and 0.31. The super-plasticizer content was adjusted for each mixture to provide a sufficient amount for efficient dispersion of the cement and silica fume particles, but also to make sure that there would be no excess of this additive that might lead to effects such as bleeding. Results show that the partial replacement of cement by silica fume increases the compressive strength of mortar but has no effect on the compressive strength of paste. Results also show that the partial replacement of portland cement by silica fume decreases the tensile strength of both paste and mortar. The reduction in the strength of paste was greater than the reduction in the strength of mortar. Results were verified by statistical analysis using hypothesis testing at a 95% confidence level. The uniaxial tensile strength results were obtained using the cementitious composites axial tensile technique (CCATT). The relation between the tensile strength and compressive strength of materials with and without silica fume was obtained. The ratios of tensile to compressive strength of paste and of mortar were decreased with increasing silica fume content.

Corrosion behaviour of steel in high alumina cement mortar cured at 5,25 and 55 °C: chemical and physical factors

Abstract: The corrosion behaviour of embedded steel was related to the composition of the pore phase in equilibrium with the hydrated phases and the porosity of the high alumina cement mortars subsequent to curing at 5,25 and 55 °C. The corrosion of reinforcements was evaluated by electrochemical techniques. The effect on corrosion of 3% by weight of cement of NaCl, added during the mixing process, and of the accelerated carbonation of mortars in CO2 atmosphere were also determined. The pH value and the chemical composition of pore fluid of plain high alumina cement (HAC) mortar cured at all three temperatures suggested that the embedded steel was in a passivated state. The resistance of HAC to carbonation and its greater potential for chloride binding by chloroaluminate formation are believed to make HAC inherently more protective to steel, relative to normal Portland cement, during ingress of chloride from external sources. High corrosion rates reported in literature for steel embedded in HAC may be attributable to bad practice, not to lack of passivity.

Acoustic emission in fiber reinforced concrete

Abstract: This investigation is aimed at diagnostic studies on the behavior at different interfaces in fiber reinforced concrete: between hardened cement paste and sand, between mortar and coarse aggregate and between concrete and fibers. Other types of internal failure include aggregate crushing, fiber rupture, and so on. Only cylindrical specimens, with varying volume percentage and aspect ratio of fibers, have been tested in compression. For quite some time additives like latexes, plasticizers, fibers and silica fume are incorporated in concrete and mortar to improve one quality or the other of concrete, but one single common objective is delaying or arresting interface cracks. This investigation attempts to relate external behavior to internal signals of distress through acoustic emission. This helps to identify critical internal distress vis-a-vis external level of stress. Further, spectral analysis of acoustic signals has been attempted in frequency domain in order to establish which types of interface failure are predominant at different stages of stress. Such understanding could enable material scientists to decide on the parameters of additives with greater confidence when developing composites with desired external response. Of interest are instrumentation and on-line data processing in order to record (a) cumulative acoustic activity and (b) spectral analysis in frequency domain at different stages of progressive loading.