ICE - Institution of Civil Engineers - Virtual Library

This chapter covers the background and history of mortar; the constituents: cements, limes, sands and other minor components; mortar requirements, varieties, properties, testing and use; and the major elements of supply, production and manufacture and site practice.

Contents

• Scope

• Introduction and historical background

• Mortar types

• The requirements of mortar

• Cements for mortar

• White cement

• Pozzolans

• Limes for mortar

• Sands for mortar

• Admixtures

• The properties of mortars

• Appearance

• The durability of mortar

• Mortar production and sourcing

• Site practice and mortar

• References

The effects of mixing procedure, testing procedure and relative proportions of constituent materials on the rheology of fresh mortar, as measured by the ViscoCorder, have been studied. Mortar shows structural breakdown, and the flow curve of the broken down material conforms to the Bingham model. The yield value and plastic viscosity vary with composition in a similar way to that shown by fresh concrete: tests with the instrument on model concrete (i.e. with no coarse aggregate) could be useful in predicting the behaviour of fresh concrete.

Permeabilities of normal and lightweight mortars have been determined and related to pore structure from mercury porosimeter analyses. It was found that lightweight mortar is only about twice as permeable as sand mortar of equal aggregate volume concentration. Permeability of mortar increases as porosity is reduced by the addition of aggregates of lower porosity. In principle, the decision to use dry aggregates is safer for the durability control of concrete mortars.

The present study explores the properties of tyre rubber ash (TRA) mortar under ordinary wet curing conditions. Tyre rubber chips were obtained and burned in an oven at a controlled temperature of 850 °C for 72 hours. The residue of the tyre rubber chips (ash) was collected from the oven and used in the mortar mixes. The TRA was utilized as partial replacement of the sand in five levels 0, 2.5, 5, 7.5, and 10% by weight of the sand. The same water to cement ratio of 0.65 was used in all mortar mixes. The properties of mortar mixes investigated include workability, setting time, compressive, tensile, and flexural strengths. The test results indicated that the TRA can be used as partial replacement of sand in mortar mixes to produce workable mortar. The workability of TRA mortar decreased with increasing the TRA content. The initial and final setting time of mortar mixes increased with increasing the TRA content. The TRA specimens showed higher compressive strengths at various curing periods up to 90 days compared with those of the control specimens. Also, the tensile and flexural strengths of the TRA mortar specimens were higher than those of the control mortar specimens.

• Introduction

• Experimental Program

• Specimens Preparation

• Results and Discussion

• Conclusions

• References

The effect of thermal expansion and contraction in masonry has been simulated using repeated stress cycles. Cylindrical specimens cast from 1:2 NHL3.5 lime mortar were exposed to air at 208° and 65% relative humidity with a CO₂ concentration of 400 ppm for 28 and 84 days respectively prior to stress cycling 40 times. Cycling did not influence the peak stress recorded from subsequent destructive compressive testing, however the un-cycled specimens absorbed more energy up to the peak stress, compared with the cycled specimens. Ion-induced electron images of the mortar structure revealed the presence of micro-cracks in the cycled mortars, suggesting the energy absorbing mechanism.

This paper presents experimental results from an ongoing study investigating the flexural bond strength, initial shear strength and compressive strength of brickwork built using natural hydraulic lime mortars. All tests were conducted in accordance with relevant standard procedures. Flexural bond strengths, with planes of failure parallel and perpendicular to bed joints, were determined by panel (wallette) tests. Bond wrench testing of stack-bonded prisms was also conducted to investigate further the material influences on flexural strength. The main parameters studied in this investigation were mortar mix design (binder : aggregate ratio; lime grade) and brick water absorption characteristics. The flexural bond strength and initial shear strength of the brickwork in general increased with mortar strength, but flexural bond strength was significantly impaired by both low and high brick water absorption. The bond wrench test was found to be a reliable, quick and easy, alternative test procedure to determine flexural strength (with plane of failure) parallel to the bed joints.

Chemicals storage in concrete silos often presents durability problems due to their chemical attack, the situation being severe due to the high concentration. The paper aims to examine the effects of ammonium salts-ammonium sulphate and nitrate, noted for their aggressive behaviour. Two laboratory programmes are reported which study the influence of ammonium solutions on PC mortar samples. Modification to mortar properties are reported. Ammonium sulphate undergoes a strong swelling that is correlated with the reduction in strength. These mortars also undergo rapid cracking after removal from solution and exposure to air. Ammonium nitrate undergoes a rapid decalcification which is accompanied by a strength loss.

• Introduction

• Experimental Programme

• Experimental Results

• Discussion

• Conclusions

• References