Mortars Workability

Masonry cements (80) are cements for use in mortars for masonry constmction. They are formulated to yield easily workable mortars and contain special additives that reduce the loss of water from the mortar to the porous masonry units. 

Concrete, Mortar, and Plaster. Citric acid and citrate salts are used as admixtures in concrete, mortar, and plaster formulations to retard setting times and reduce the amount of water requited to make a workable mixture (172—180). The citrate ion slows the hydration of Portland cement and acts as a dispersant, reducing the viscosity of the system (181). At levels below 0.1%, citrates accelerate the setting rate while at 0.2—0.4% the set rate is retarded. High early strength and improved frost resistance have been reported when adding citrate to concrete, mortar, and plaster. 

Abdelrazig, Sharp El-Jazairi (1988, 1989) prepared a series of mortars based on a powder blend of MgO and ADP with a quartz sand filler. They were hydrated by mixing with water. A mortar I (MgO ADP silica water = 17T 12-9 70-0 12-5), with a water/solid ratio of 1 8, formed a workable paste which set in 7 minutes with evolution of ammonia. The main hydration product, struvite, was formed in appreciable amounts within 5 minutes and continued to increase. Schertelite also appeared, but only in minor amounts, within the first 5 minutes and persisted only during the first hour of the reaction. Dittmarite appeared in minor amounts after 15 minutes, and persisted. 

Plasticiser Improving workability, consolidation of fresh mortar Milk, egg white, fats, oils, sugar, colophony... 

Although the mix design of latex-modified mortar and concrete is done in much the same way as that of ordinary mortar and concrete, properties such as workability, strength, extendibihty, adhesion, watertightness and chemical resistance are controlled by the polymer-cement ratio rather... 

Masony cements are hydraulic cements designed to have improved workability for use in mortar for masonry construction. The standards are given in... 

There are many deficiencies associated with unmodified cement mortars, such as the potential for incomplete hydration (especially in thin sections), poor adhesion and the high water level needed for adequate workability. Above all, cement is a brittle product with low flexural strength, impact resistance and abrasion resistance (Rohm Haas, 1989). 

Acrylic emulsions (or acrylic latices) are characterised as high-solids polymers having a film-forming temperature at or below room temperature (Lavelle, 1986). They have excellent hydrolysis resistance compared with other resins and are well suited as modifiers for portland cement mortars. Studies have shown that certain acrylic latices impart excellent workability at lower water demand, thin section adhesion and toughness, improved flexural strength and tensile strength and outstanding adhesion (Lavelle, 1983). 

The workability of the fresh mortars and the properties of the hardened mortars are determined by the mix composition (binder, water, traditional aggregate, polymeric granulate, additives) in the same way like in normal lightweight mortar technology. The dense structure of the grains is advantageous as it makes it unnecessary to take into account the water suction of the aggregate. 

Polymer modified lightweight cement mortar (PLCM) with plastics waste as aggregate is widely used as substrate mortar layer on the reinforced concrete wall for external ceramic wall tile installations instead of the ordinary cement mortar conventionally used. The reasons that this mortar is popularly used in building site are it s own lightweight and excellent workability for troweling. 

Workability of ordinary plain cement mortar is generally estimated with the flow test by Japanese Industrial Standard (JIS). But this test method can not estimate sufficiently the workability of PLCM with visco-elastic behavior. 

Hydresol . [BASF AG] Niq)hthalene sulfonic or phenol-sulfonic adds/form-aldehyde condensates plasticizers for mine binders, for itt proving workability of mineral-bond mortar and ctmcrete. 

The particle shape of sands produced by crushing dense limestones tends to be angular and cubical. This is satisfactory from the viewpoint of the properties of the hardened mortar, but tends to produce a somewhat harsher and less workable fresh mortar than many naturally occurring silica sands, which generally have a more rounded shape. 

The quality of building limes is specified in [22.6]. It requires minimum values for standard mortars produced from lime putties — namely penetration and air content — and lists water demand and water retention as parameters that customers may request. It also specifies a minimum volume yield of putty per kg of quicklime. Building limes must also be sound (i.e., pass the popping, pitting and expansion tests). A workability test, based on the spread of a standard mortar on a jolting table, was specified in the 1972 edition of BS 890 [22.11], but is no longer included. 

A discovery that air-entrainment not only improved workability but also increased frost resistance led to the use of mortars with high levels of air entraining agents. While the soft properties of such mortars were good, very high levels of entrained air resulted in poor bond strengths, and lead to the failure of a number of walls under tension and/or flexion. Modem specifications limit the level of entrained air. 

Mortar should never be re-worked when it begins to stiffen. Such practice reduces workability, compressive strength and bond strength. 

Good workability is important to ensure that the mortar is easily applied and can be effectively worked into the joints and crevices of the background material. A high degree of cohesiveness ensures that the mortar adheres to the trowel and to the background. It is also essential when using mechanical spraying equipment. 

Lime-based mortars have excellent workability and plasticity, a high degree of cohesiveness and spread easily under the trowel. These properties help to increase productivity and minimise wastage by droppings. They are eminently suitable for use with mechanical spraying equipment. 

Air-entrainment occurs when a surfactant is added to a mortar to increase the level of entrained air, thereby improving its workability. 

Plasticiser is an agent, which may be added to mortar or concrete to improve its workability by increasing air entrainment. 

Whiting is a finely powdered product produced by milling and classifying limestone (generally chalk). The nominal top size varies from 10 to 75 pm. Workability is a measure of the ease with which a fresh mix of concrete or mortar can be handled and placed. 

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