For projects, the newly mixed mortar should have good workability, and the hardened mortar should have the required strength, bending strength at the bottom face, little deformation and durability.
The workability of fresh mortar refers to the broad properties of mortar that is easy to manufacture and good for quality, including mobility and water retention. Mortar with good mobility is easy to set thinly and evenly on bricks and binds well to the floor.
a. mobility (consistency)
Mortar mobility is the property that mortar can flow under the action of dead weight and external force. Fluidity is expressed by the “degree of sinking”, usually determined by the consistency of the mortar. The greater the degree of sinking, the better the maneuverability.
Mortar mobility should be determined by the type of masonry, construction conditions and weather. The consistency of the masonry mortar should be selected as per the requirement of the project.
b. water retention
Water retention of mortar refers to the property of mortar to retain moisture. When mortar with good water retention is used in transportation, erecting and pavement, water will not drain out of the mortar as soon and the required consistency can be maintained. It is easy to manipulate to keep a certain amount of water in the mortar and also guarantee the normal hydration of the cement to maintain the strength of the masonry.
The water retention of mortar is expressed by the layering degree, which is measured by the mortar layering degree instrument. The mortar with good water retention has a layering degree of 10-30 mm, and if it is more than 30 mm, the water retention will be poor and easy to disassemble; Mortar whose layering degree is less than 10 mm is not good for construction. Based on several experiments, the layering degree of cement mortar should not exceed 30 mm, and the layering degree of cement mix mortar should not exceed 20 mm.
Hardened mortar should have great strength which is expressed by the strength grade. Compressive strength is the mainstay of mortar strength. strength grade of mortar, expressed by FM, determined by the compressive strength average (MPa), measured by means of treating a group of six cube samples with a length of 70.7 mm for 28d, by the standard test method.
Strength grades of mortar include: M20, M15, M10, M7.5, M5 and M2.5, six grades.
The strength of mortar is tied to its surface material. For ordinary cement mortar, the following equation can be used to calculate its compressive strength.
Brick and stone masonry is a concrete unit made up of multiple blocks that are bonded together by mortar as a whole. Thus, it is essential that the mortar should have a certain adhesion stress on the bricks and stones. Generally, the higher the compressive strength of the mortar, the greater its adhesion stress. In addition, its adhesion stress is related to the surface, cleanliness and moisture content of bricks and stones, as well as construction and curing conditions. For example, making bricks requires water, and a surface without clay will improve the adhesion tension and ensure the quality of the masonry.
It is easy for mortar to deform when bearing loads or changes in temperature. If it is deformed too much or unevenly, the quality of the masonry and surface will be reduced and cause shrinkage and cracking. When fine aggregate is used for mixing mortar, its deformation is larger than that of ordinary mortar. In order to prevent cracks caused by uneven shrinkage deformation, hemp cut, paper strip and other fabric materials can be mixed into the surface mortar.
Mortar’s durability refers to the property to withstand wear and tear over long periods of use. Hydraulic masonry that normally contacts water must be impermeable and frost resistant, so the impermeability and frost resistance of hydraulic masonry must be considered.
a. frost resistance
Mortar’s frost resistance refers to the property to resist the freeze-thaw cycle. The mortar has solidified and is damaged because the water in its pores expands and breaks the pores as it freezes. Thus, dense mortar and mortar with closed pores have good frost resistance. In addition, factors affecting the frost resistance of mortar also include cement type, strength grade and water-cement ratio.
The frost resistance of mortar is the property of resisting the infiltration of pressurized water. It is mainly related to the density and size and composition of the internal pores. The inside of mortar and cellular structures form connecting pores and, when it is molded, pores, all of which can cause water seepage of the mortar.