Sprayed Mortar Research Articles

Effects of selected retarders on workability window and other properties of cement-based sprayed mortars

Setting reducing agents were studied with respect to rheological properties of sprayed mortars based on fast-setting cement binder. The aim was to slightly delay the fast-setting effect caused mainly by tricalcium aluminate presence in order to adjust the workability window resulting in improved pumpability. Main experiments were performed using rotational rheometer and powder X-ray diffractometer. Additionally, 7day, 14day and 28day strength tests were done. The results show that chosen chemicals work as retarders, but not in required extent. Moreover, apart from the usual slower development of the strength due to the presence of retarder, at applied amounts, some of them can even have undesirable side effects such as causing weaker overall structure of the cured specimens.

Experimental study of bond behavior on sprayed and poured mortar–brick interface with latex bonding agent under conventional and humid environments

Sprayed mortars are able to enhance masonry walls, particularly for improving the resistance of the existing building stock to horizontal forces such as seismic. This is the case of numerous neighborhoods around the world constructed using load-bearing masonry walls before the 1950s. These mortars are sprayed on site and, to strengthen the interface, for example, latex interface bonding agents are applied between the sprayed mortar and masonry walls. Latex, being sensitive to ambient humidity, undergoes changes in its mechanical properties that directly impact the entire structure of the enhanced wall. But this crucial influence of ambient humidity on the latex layer has often been scarcely analyzed in previous studies. To overcome this gap, this research paper conducts an experimental investigation on the interfacial behavior under different humidity curing environments. It also compares interfaces formed through pouring and spraying methods. Several samples with latex interfacial bonding agents were tested using direct tension and direct shear tests to obtain stress–strain curves. Bond strength, fracture energy, and stiffness were determined using the traction separation method (TSL). This experiments found out that ambient humidity conditions significantly affected interfacial properties. In most cases, conventional curing environments resulted in higher peak stresses and fracture energies compared to humid conditions. Overall, sprayed mortar samples exhibited better interfacial properties than poured ones. Sprayed mortar samples demonstrated higher overall stiffness. The experimental results were fitted using three TSL models, with Schneider’s model providing the most accurate representation of interfacial behavior after optimization.

The role of SCM’s on rheology of sprayed mortar

The role of various SCM’s on rheology of fresh sprayed mortar was studied. The mix design was inspired by recent trends in SCM’s with use of ground limestone, calcined clays and natural pozzolanas. New formulations were correlated to commonly used SCM’s like blastfurnace slag and fly ash. Sprayed mortar designed mostly for thin profile coatings is demanding material in terms of rheology requiring good adhesion, pumpability, shootability, stability after spraying, low segregation and minimum rebound. Particle packing model was used for sprayed mortar mix design. Time and shear rate dependent rheological parameters were calculated using conventional models to describe the properties of fresh sprayed mortars. A procedure for determining the segregation of the mortar using a rheometer was proposed.

Bond Strength Tests under Pure Shear and Tension between Masonry and Sprayed Mortar.

Sprayed mortar or shotcrete is a construction technology that could enhance existing masonry buildings’ resilience by reinforcing low-safety load-bearing walls. Many factors affect the resistance of shotcrete-reinforced structures. One of the most important is the bond strength at the interface between the shotcrete and the reinforced wall. According to previous technical literature, bond strength usually has two evaluation criteria: shear and tensile strength. The experimental campaign described in this article focused on the bond strength between sprayed mortar and three masonry materials without the influence of normal force or constraint, as well as the roughness of these materials. The analysis of these tests focused on determining the relation between bond strength, roughness, and material strength. The analyses revealed that material strength has a more significant effect on bond strength than roughness, and bond strength is related to shrinkage of the materials. On the basis of previous theories, these researchers found that when there is no obvious influence due to normal force and constraint, the shear strength and tensile strength are different, and the shear strength is likely to be the cohesion force of the two materials. Finally, this article concludes with a novel logarithmic relationship between these strengths.

Research on coating technology with wet-process sprayed mortar: waste and productivity

Abstract The mechanical application of mortar is as an adequate solution to minimize the problems in the execution of internal and external coating of the buildings. However, few scientific studies address the gains in efficiency afforded by mechanization as well as the scarce parameters of waste, productivity and quality that could contribute to choosing this technology. This article aims to characterize the presented constructive technology and to investigate the waste of mortar (percentage of losses and consumption) and the productivity of the labor in the execution of internal and external coating for sealing in the application of wet-process sprayed mortar. Investigations were carried out in 08 construction works, which presented results of up to 150% and 0.18h/m2 for, respectively, loss of industrialized mortar and labor productivity. Thus, the present research contributes to the advancement of the knowledge about the wet-process sprayed mortar by increasing the understanding of the technology. Other important contributions are the indicators of losses and productivity and their detailed measurement, which are efficient tools to assist the companies in the decision-making by adopting this technology as well as in the management of the activities during the execution process.

Losses and Productivity Parameters for Cladding Technology with Wet-Process Sprayed Mortar

Background and Objective:The wet-process sprayed mortar is a potential solution to minimize the traditional application negative points. However, its use is still incipient and a recent technological innovation in several regions of Brazil. Few available parameters that attest gains to subsidize the budget, design, and execution of cladding are systematized. This paper aims to evaluate the industrialized mortar loss and labor productivity in the execution of internal and external cladding for buildings.Methods:The first step was to define the elements to characterize the constructive cladding technology with mechanical projection of mortar and method for effective data collection. The second step consisted in the accomplishment of the field research, which took into account the case studies in 08 buildings under construction. The third step intended to describe the best practices highlighted in the construction works analyzed and the fourth step described the identification of actions able to succeed in the implementation and operation of the system.Result:The results allowed verifying industrialized mortar loss varying from 6.38% to 150.02%, as well as masons’ productivity from 0.18M’hr/m2up to 5.91M’hr/m2. The present research also made it possible to identify factors influencing the increase in the loss indicator, such as the fresh mortar consistency, failure in the transport and control of bagged materials, and high thicknesses in the cladding layer. As for the factors that favored productivity, it is important to highlight: the experience of the masons involved, the mortar application to the windows, and good logistics for the transportation of bagged goods.Conclusion:Identification of the best practices, opportunities to improve production management, and obtainment of quantitative references comprise the main contributions of this research, which may help in adoption of this technology and solution of similar problems by construction companies.

Influence of production systems on the properties of fresh and hardened shotcrete

Abstract In modern shotcrete operations, the mixing and pumping steps are carried out using different production systems and equipment. This adds an element of uncertainty to the process because of variables such as mixer type, rotation speed, mixing time, etc. As a result, this may result in changes to the characteristics and properties of both fresh and hardened sprayed mortar and may ultimately impair the performance of the rendering material. This study assesses the influence of production systems, particularly the mixing process, on the properties of fresh and hardened sprayed mortar. The methods used comprehend the collection and testing of mortar samples produced in wet-mix and dry-mix shotcrete systems, as well as a pre-packaged mortar batched and mixed in a laboratory mixer under controlled conditions according to the manufacturer’s instructions. Results were processed using analysis of variance (ANOVA) and multiple comparison of means using Fisher’s method. A statistically significant difference was observed in the flow table index, water retention, flexural strength and capillarity coefficient of the mortars produced using wet- and dry-mix systems.

Rheological and thermal properties of aerated sprayed mortar

This paper studies the rheological properties in aerated cement pastes in order to develop an aerated sprayed mortar with low thermal conductivity. For this purpose, different mixtures of cement with additions of metakaolin (MK) and sepiolite (SP) were tested. In addition, influence of yield stress on build-up thickness, as well as expansion speed and pore network were studied using cement pastes aerated with aluminum powder. At the same time, the volume increase during expansion, water retention and yield stress of the fresh foamed cement pastes were studied to characterize the fresh mortar. Results obtained show that the incorporation of siliceous fly ashes (SFA) in ordinary Portland cement together with additions of MK or/and SP provided the largest expansion speed increase and the lowest density of the aerated mortar. Pastes with greater yield stress show higher thermal conductivity but are better to be pneumatically gunited due to its bigger build up thickness. The most suitable paste from all them was selected, sprayed and aerated over ceramic bricks, checking the results on site. Results obtained by means of these tests confirm that is possible to spray an aerated mortar over vertical surfaces. In addition, this mortar has acceptable thermal insulation properties to be used in chambers of building façades and for external wall thermal insulation systems (EWIS).

Experimental assessment of Textile Reinforced Sprayed Mortar strengthening system for brickwork wallettes

This work explores the feasibility of strengthening masonry with Textile Reinforced Mortar (TRM) by projecting it to save application time. Nineteen tests on masonry samples strengthened with TRM have been carried out to assess this new application method. Different mortars and fibre grids were considered for studying their influence and applicability with this new technique. Three points bending tests have been performed on the specimens to compare the flexural strength between cases with manually applied mortar (TRM) and sprayed application (TRSM) of the mortar layer. It was noticed that the strengthening mortar has a significant influence on the failure mode. Results show a remarkable (between 2 and 6 times more) productivity increase when using TRSM and a load-bearing capacity rise for the cases with larger grid spacing and projectable mortar when using TRSM instead of TRM. Greater ductility values were also observed for the TRSM cases in comparison with the analogue TRM cases (same grid and mortar).

Low-volume wet-process sprayed concrete: hardened properties

This paper, which reports on part of a 3-year research project into wet-process sprayed mortars and concretes for repair, investigates the hardened performance of wet-process sprayed fine concretes. It follows on from an earlier paper by the authors on the performance of hardened wet-process sprayed mortars and some comparisons with these are made here (Austin SA, Robins PJ, Goodier CI (2000). Magz Concr Res 52:195–208). Work has also been completed by the authors on the pumping and rheology of the fine concrete mixes presented here (Austin SA, Goodier, CI, Robins PJ (2005). Mater Struc, RILEM 38:229–237). Nine laboratory-designed fine concretes were pumped and sprayed through a wet-process piston pump and one through a dry-process pump. The properties measured included compressive and flexural strength, tensile bond strength, hardened density, elastic modulus, sorptivity and drying and restrained shrinkage. In situ test specimens were extracted from 500 × 500 × 100 mm deep sprayed panels. Hardened property tests were also conducted on corresponding cast specimens and, where possible, on specimens that had been sprayed directly into a cube or beam mould. The compressive strengths of the cast cubes, although very similar, were usually slightly greater than the in␣situ cubes, the opposite of what was found for wet-sprayed mortars (Austin SA, Robins PJ, Goodier CI (2000). Magz Concr Res 52:195–208). Inconsistent results for compressive and flexural strengths obtained from spraying directly into a steel mould suggest that this method is not as reliable when using a piston pump as it is when using a low-output worm pump (Austin SA, Robins PJ, Goodier CI (2000). Magz Concr Res 52:195–208). The bond strength of all the mixes exceeded 2.1 MPa at 7 days. The values for modulus of elasticity, when compared with the compressive strength, were similar to published data for this relationship. The sorptivity values showed only a slight relationship with the compressive strength. The mixes exhibited a wide range of drying shrinkage, but the data from the restrained specimens suggest an actual repair is influenced as much by ambient conditions as it is by the mix proportions.

Coal fly ash-containing sprayed mortar for passive fire protection of steel sections

The present article addresses the possible use of coal fly ash as the chief component of sprayed mortars to fireproof steel structures. A pilot wet-mix gunning rig was specifically designed and built to spray different pastes on to sheet steel and sections with different surface/volume ratios. After gunning, the specimens were placed in a furnace and subjected to standard fire resistance testing. Product fire resistance was calculated from the test results. The mortar used in this study, with a high fly ash content, was found to have acceptable mechanical properties as well as afire resistance potential comparable to those of commercial passive fire protection products.

The performance of hardened wet-process sprayed mortars

This paper, which reports on part of a three-year research project into wet-process sprayed mortars and concretes for repair, investigates the hardened performance of wet-process sprayed mortars. Seven commercially available preblended repair mortars were pumped and sprayed through a worm pump, three through a piston pump and two through a dry-spray machine. A laboratory-designed mortar was also worm and piston pumped. The properties measured included compressive and flexural strength, tensile bond strength, hardened density, modulus of elasticity, air permeability, sorptivity, and drying and restrained shrinkage. In situ test specimens were extracted from 500 mm × 500 mm × 100 mm deep sprayed panels. Tests were also conducted on corresponding cast specimens and, where possible, on specimens that had been sprayed directly into a cube or beam mould. A new test to quantify the degree of reinforcement encasement has been developed and an initial investigation into the measurement of the restrained shrinkage of in situ repairs is presented. The compressive and flexural strengths of the laboratory mix were comparable to those of the best of the commercially available preblended mortars. The values for modulus of elasticity, when compared with the compressive strength, were lower than published formulae for this relationship would suggest, especially at lower strengths. The air permeability of most of the mortars was lower than that for normal wet-cured concrete and decreased with an increase in compressive strength. The sorptivity values showed no clear relationship to the compressive strength. The type of wet-process pump was found to have little effect on the in situ compressive and flexural strengths but did affect the bond strength, although this was mainly because of the stream velocity and w/c ratio rather than the pumping process. The pump type also affected the reinforcement encasement, with higher stream velocities producing better encasement. The mixes exhibited a wide range of drying shrinkage, but the data from the restrained specimens suggest an actual repair is influenced as much by ambient conditions as it is by the mix proportions.

The rheological performance of wet-process sprayed mortars

This paper, which reports on part of a three-year research project into wet process sprayed concrete for repair, examines the influence of rheology on the pumping and spraying of mortars. The performance of seven commercially available prepackaged repair mortars and six laboratory-designed fine mortars was examined using the Tattersall two-point and Viskomat rotational viscometers, the pressure bleed test, the slump test, a build test and a vane shear strength test. These tests were used to form a rheological audit of each mortars. The two-point apparatus was successful with low-workability mortars, and their flow resistance and torque viscosities were determine. These parameters were also obtained with the Viskomat, although problems were encountered owing to the low workability of the mortars. The pressure bleed test measured both the rate and the total volume of liquid emitted from the mixes, while the vane shear strength test provided an instantaneous reading of the shear strength of the mortars and is compared with their slump. The mortars were pumped and sprayed through a worm pump to assess their suitability and to measure their adhesion to a substrate by build thickness. This value is a measure of sprayability and is converted into values of maximum shear and bending stress, which are then compared with the workability parameters in order to determine their interrelationship.