Introduction

Mortars incorporating masonry cements are used for bedding masonry units and also for rendering and plastering. In 1988 the CEN Technical Committee responsible for Cements and Building Limes (TC 51) charged its Working Group 10 to produce a Standard for Masonry cements and for the test methods to support that Standard.

Test methods for setting time, soundness and strength are common requirements in most cement standards. However, where the cement is specifically designed to adhere to and subsequently provide a good bond with masonry units, it is important that an adequate level of workability is achieved. In contrast to the concept of workability as applied to concrete, workability in mortars is not just a question of adjusting the "wetness" of the mortar by adding more or less water. In masonry work, the craftsman requires rather more of his materials in that he expects them to flow easily from the trowel and to spread on to the masonry unit evenly and without segregation. It is only when these properties are present that he can expect to achieve the consistent degree of bonding necessary to produce durable watertight joints and renderings.

The appropriate RILEM Committee considered that workability comprised two main components, notably: consistence and plasticity. They defined these components as follows:

Consistence: That property of a mortar by virtue of which it tends to resist deformation.

Plasticity: That property of a mortar by virtue of which it tends to retain its deformation after reduction of the deforming stress to its yield point.

Consistence is a measure of wetness and is measured using a penetration device, but that plasticity required a more dynamic assessment such as could be achieved by using apparatus which caused the mortar to move. However, in order to obtain any meaningful numerical measure of plasticity, it was adjudged important to ensure that the testing for this characteristic was carried out on mortars where the consistence had been controlled to a narrow band.

Since the testing procedure adopted in the CEN Standard EN 413‑2:1994, Masonry cement - Part 2: Test methods involved the preparation of a mortar using standard sand and with sufficient water to achieve a narrow band of consistence as assessed using a plunger (penetration) test, this was considered as the starting point for the work to assess workability, or as was deemed more appropriate "cohesivity".

Early work involved measuring the time taken for a mortar of standard consistence to flow between two points in the AFNOR workability meter. This method was incorporated into EN 413‑2:1994 as a test method, but on account of the limited amount of experience available no limits were set in the Masonry cement Prestandard ENV 413‑1. Subsequently, further testing revealed significant calibration problems between laboratories and consideration was given to the use of a flow table as an alternative means of providing the dynamic component of the test. This document deals with the development of the test using flow tables.

PD CEN/TR 13933:2023

Masonry cement. Testing for workability (cohesivity)

Current

Published:

30 Nov 2023