Showing papers on "Mortar published in 1998"

Polymer-based admixtures

Abstract: The concept of polymer modification for cement mortar and concrete is not new, since considerable research and development of polymer modification have been performed for the past 70 years or more. As a result, various polymer-based admixtures have been developed, and polymer-modified mortar and concrete using them are currently popular construction materials because of their good cost-performance balance. This article summarizes the classification of polymer-based admixtures, the principles of polymer modification by the use of polymer latexes, redispersible polymer powders, water-soluble polymers and liquid polymers, the properties and applications of polymer-modified mortar and concrete, recent research and development activities, and standardization work.

Workability, mechanical properties, and chemical stability of a recycled tyre rubber-filled cementitious composite

Abstract: The workability and mechanical properties of mortar containing shredded automobile and truck tyres were evaluated. Two different shapes of rubber particles were used as constituents of mortar: (1) granules about 2 mm in diameter, and (2) shreds having two sizes which were, nominally, 5.5 mm×1.2 mm and 10.8 mm×1.8 mm (length×diameter). As expected, the geometry of the rubber particles influenced the fracture behaviour of rubber-containing mortar. The addition of rubber led to a decrease in flexural strength and plastic shrinkage cracking of mortar. The crack width and crack length due to plastic shrinkage were reduced for mortar containing the 10.8×1.8 mm rubber shreds compared with a mortar without shreds. The rheological properties of the mortar containing rubber shreds were comparable to those of a mortar without rubber and yielded lower plastic viscosity than a mortar containing 25.4 mm×15 μm (length×diameter) polypropylene fibres. The alkaline stability of rubber in mortar was also evaluated by immersing rubber shreds in NaOH and Ca(OH)2 solutions for 4 mon and the results showed that there is less than 20% change in stress and strain value. The findings of the research suggest that automobile and truck tyres can be recycled by shredding and incorporating them into mortar and probably concrete for certain infrastructural applications. © 1998 Chapman & Hall

A water sorptivity test for martar and concrete

Abstract: This paper describes a test rig to measure the uni-directional water absorption of mortar and concrete. The test data acquisition is controlled by purpose written software installed on a PC and the results are utilised directly to obtain the sorptivity measured in g/mm2/min1/2. As an example the apparatus was used to obtain the sorptivity of mortar in which the ordinary Portland cement was partially replaced by ground waste brick obtained from different sources. The results presented demonstrate the validity of the test, and the apparatus and the methodology are shown to be of sufficient sensitivity in detecting the differences between the sorptivities of the various mortars tested. The variation in the sorptivity with curing time and mixture composition was determined. The paper also gives the results of total water absorption test conducted on the sorptivity test specimens, after being reconditioned, and the results of compressive strength tests for all the mortars investigated.

Corrosion of reinforcement steel embedded in high water-cement ratio concrete contaminated with chloride

Abstract: The aim of this investigation was to examine the role of internal chloride on the corrosion behaviour of steel in ordinary Portland cement (OPC), and sulphate resistant Portland cement (SRPC) mortar mixes of higher water-cement (w/c) ratios. For this purpose, the steel electrodes embedded in mortar specimens were subjected to short-term electrochemical monitoring. On completion of electrochemical monitoring, pore solution was extracted from the specimens for analysis. For the purpose of comparison, pore solution was also extracted from separate OPC and SRPC cylindrical mortar specimens hydrated in an environment isolated from the atmosphere. Results from microanalysis using scanning electron microscope (SEM) are also reported. The results demonstrated that mortars prepared with a cement of high tricalcium aluminate (C 3 A) content, even when the w/c ratio of the mix was maintained at 0.70, still passivated the steel embedded in it even in the presence of chloride as high as 1% by weight of cement. Under a similar condition, the steel embedded in mortar prepared with a cement of low C 3 A content was unable to passivate the steel electrode. The special protection mechanism by the lime-rich layer as proposed by Page for low w/c ratio concretes is also valid for the steel embedded in high w/c ratio mortar. The type of exposure condition (e.g. exposure to atmosphere) during the hydration period strongly influences the hydroxide ion concentration in the pore solution, while this has no effect on the freechloride concentration in the pore solution. This study reconfirms the significance of the C 3 A phase of cement in respect to chloride-binding processes.

Effect of slag on expansion due to alkali-aggregate reaction in concrete

Abstract: The efficacy of ground granulated blast furnace slag in controlling expansion caused by alkali-aggregate reaction was evaluated using both concrete prism and accelerated mortar bar testing. Six aggregates were included in the program; four of these were classified as alkali-silica reactive (siliceous limestone, sandstone, greywacke, and granite), one as alkali-carbonate reactive (dolomitic limestone), and one as nonreactive (dolostone). The partial replacement portland cement with slag in the range of 25-65% was effective in retarding the rate of expansion and limiting the ultimate expansion at 2 years in concrete prisms cast with all four alkali-silica reactive aggregates. However, the minimum level of slag required to control expansion to an acceptable level, (for example, 0.04% at 2 years) was found to vary depending on the nature of the aggregate and the amount of alkali present in the concrete. There appears to be a reliable correlation between the expansion of mortar bars after 14 days storage in 1M NaOH at 80 deg C and the expansion of concrete prisms after 2 years storage over water at 38 deg C. The accelerated mortar bar test appears to be an appropriate tool for determining the minimum "safe" level of slag required for a particular reactive aggregate source. The use of slag also reduced the initial rate of expansion of concrete prisms containing the alkali-carbonate reactive (ACR) aggregate. However, the expansion at 2 years exceeded 0.20% for all slag levels tested (25-65%), and this final expansion was actually greater for concretes with 25-50% slag than for the control concrete. The expansion of mortar bars was less than 0.10% at 14 days for all the mixes tested, which confirms the unsuitability of this test for detecting ACR aggregates.

Alkali-silica reaction--part 2: the effect of chemical admixtures

Abstract: Many aggregates are susceptible to the alkali-silica reaction. As a result of this reaction, mortar bars and concrete elements containing portland cement expand. In order to limit this expansion, chemical admixtures that interfere with the alkali-silica reaction can be introduced into the mixing water. The research discussed below describes how several of these chemical admixtures affect mortar-bar expansion. Mortar bars containing any of several chemical admixtures in the mixing water at initial molar concentrations of 1 or 2 were subjected to ASTM C 1260 tests. After the expansion test, samples were prepared from each of the mortar bars and examined in a scanning electron microscope with EDX capabilities. The following chloride salts and hydroxides were used: NaOH, KOH, LiOH, NaCl, KCl, LiCl, CaCl2, MgCl2, and AlCl3. For a given initial molar concentration, the expansion test results indicated that the chloride salts with monovalent cations were the most damaging, followed by those with divalent and trivalent cations. These results are in agreement with a theoretical model presented in a previous paper that explains the volume change behavior of the reaction product gels. This model attributes the swelling of the reaction product gel to double-layer repulsion forces.

Water extraction out of mortar during brick laying: A NMR study

Abstract: The water extraction out of mortar during brick laying was studied using nuclear magnetic resonance. The experiments show that using a fired-clay brick, the water is extracted out of the mortar within 3 minutes, whereas in the case of a sand-lime brick this takes about 10 minutes. Prewetting a fired-clay brick hardly affects the water extraction, whereas prewetting a sand-lime brick slows down the water extraction, although the effect is small. The extraction process is slowed down only if the bricks are almost fully saturated. These effects are explained with the help of computer simulations. The final moisture content of the mortar is shown to depend on the suction of the brick and thereby on the equilibrium moisture content of the brick. By adding a water retention agent to the mortar, the extraction process seems to slow down, although the final moisture content of the mortar is not changed. The water extraction experiments suggest that the suction of the mortar which is formed depends on the water extraction rate and thereby on the type of brick that is used in the extraction experiment. Petrographic analyses indicate that the extent of bonding between the brick and the mortar is different for fired-clay brick and sand-lime brick.

Poly (Vinyl Alcohol) stabilized acrylic polymer modified hydraulic cement systems

Abstract: Mortar formulations comprising a hydraulic cement and a PVOH stabilized acrylic latex or a spray dried redispersible powder made from the PVOH stabilized acrylic latex are disclosed. These include formulations suitable for use as tile mortars, patching mortars, EIFS base coats and grouts. An acrylic latex that, when formulated with hydraulic cement, has performance advantages over other latex resins in mortar, patch and exterior insulation and finishing systems. The spray dried, redispersible acrylic emulsion polymer that, when formulated with hydraulic cement, has comparable or better performance than a liquid latex in mortars and patches.

Triaxial behavior of high-strength concrete and mortar

Abstract: Triaxial axisymmetrical compression tests were performed on cylinders of ultra-high-strength mortar. The matrix was reinforced with straight steel fibers (6% by volume) and had a uniaxial compressive strength of 165 MPa (24 ksi). Comparisons were made with similar triaxial strength results on plain high-strength concrete (HSC) and mortar. The Coulomb friction failure criterion was applied to fit the data. The brittle compressive failure of HSC was reflected in the appearance of the failure criterion. The angle of friction governing the behavior under small confinement pressures equaled 51 deg (0.9 rad) instead of 37 deg (0.6 rad), which is typically seen for normal strength concrete. Under increasing confinement pressures, the angle of friction reduced to 30 deg (0.5 rad), attributable to the fact that the crack growth in HSC is only slightly influenced by the aggregate. Finally, the axial and lateral strains corresponding to the ultimate triaxial load were assessed in order to predict the deformations of confined HSC.

Arrangement for supporting mortar shell into barrel

Abstract: The invention relates to an arrangement for supporting a mortar shell into the barrel of a mortar weapon by using a separate support piece fixed to the tail of the mortar shell. In the arrangement the support piece is attached to the tail of the mortar shell with a mechanical joint provided by a separate connecting element (7), the connecting element being manufactured of such material and constructed in such a way that it fractures when the charge of the mortar shell is fired, allowing the mortar shell (1) to detach from the support piece (8).

Effect of GGBFS Particle-Size Distribution on Mortar Compressive Strength

Abstract: This paper presents the results of an investigation into the influence of particle-size distribution (PSD) of ground granulated blast-furnace slag (GGBFS) on the compressive strength of slag mortar. The PSD of the GGBFS powder was defined by the parameters of the Rosin-Rammler distribution function, namely, position parameter, \ix\d0, and slope \in. These parameters describe the fineness and the size range characteristics of the PSD, respectively. Samples of GGBFS with different PSDs were prepared using a method by which a commercially available GGBFS sample was first separated and then recombined into predetermined proportions. The results showed that varying the PSD of the GGBFS by keeping \in constant and increasing \ix\d0 decreased the compressive strengths of mortar mixes. Varying \in at a constant \ix\d0 was found to produce only a small change in compressive strength. However, at 70% GGBFS replacement, and for both water/cement ratios considered, the mortar mix containing the GGBFS sample with the widest range of distribution showed the highest strength at 28 days of age.

A penetration test to study the mechanical response of mortar in ancient masonry buildings

Abstract: A simple method for studying the mechanical response of the mortar in existing masonry buildings is presented herein. The method is based on the measurement of the penetration depth increment of a steel probe (4 mm diameter) at each hammer blow (impact energy=2.2 J). Numerous tests were carried out on different laboratory specimens in order to formulate a relationship between the compressive strength and the probe penetration rate, and a series of tests on actual masonry elements confirmed that the proposed relationship is sound.