Mortar shrinkage refers to the shrinkage phenomenon caused by the volume change caused by water evaporation and cement hydration during the preparation and use of mortar. Shrinkage of mortar is an important index affecting mortar performance and construction quality. High mortar shrinkage may lead to problems such as mortar cracking, deformation, hollowing, etc., seriously affecting the service life and safety of buildings. Therefore, controlling the shrinkage of mortar is a very important link in the application of mortar.

Reasons for mortar shrinkage

Shrinkage caused by water evaporation

The moisture in the mortar will gradually evaporate over time, which will cause the volume of the mortar to shrink, resulting in shrinkage. Especially in a dry and well-ventilated environment, the mortar shrinks faster.

Shrinkage due to cement hydration

Cement hydration is the process in which cement reacts with water to form hydrates. This process releases heat, which causes a change in the volume of the mortar, resulting in shrinkage. The speed of cement hydration depends on factors such as the type and content of cement and the ratio of cement to mortar.

Thermal expansion and contraction caused by temperature changes

Temperature changes are also an important factor causing mortar shrinkage. Mortar expands when it is exposed to high temperatures; conversely, it contracts when it is exposed to low temperatures. This thermal expansion and contraction are inevitable, but its influence can be reduced by controlling the temperature of the mortar.

The test method of mortar shrinkage

To control the shrinkage of mortar, it is necessary to use corresponding test methods to evaluate the shrinkage performance of mortar. Common mortar shrinkage test methods include linear shrinkage test, volume shrinkage test, drying shrinkage test, stability shrinkage test, etc.

Linear shrinkage test

The linear shrinkage test refers to the measurement of the length change of the mortar under fixed temperature and humidity conditions. This test method can reflect the drying shrinkage of mortar and the shrinkage caused by cement hydration. During the test, it is necessary to prepare a certain length of mortar sample and measure the length change of the sample through precision measuring equipment under constant temperature and humidity conditions, to calculate the linear shrinkage rate.

Volume shrinkage test

Volume shrinkage test refers to the measurement of the volume change of mortar under fixed temperature and humidity conditions. This test method can more comprehensively reflect the shrinkage performance of mortar. During the test, it is necessary to prepare a mortar sample of a certain size and measure the volume change of the sample through precision measuring equipment under constant temperature and humidity conditions, to calculate the volume shrinkage.

Drying shrinkage test

The dry shrinkage test refers to the measurement of the dry shrinkage of the mortar under the condition that the relative humidity is lower than 50%. This test method can more directly reflect the shrinkage performance of mortar in a dry environment. During the test, it is necessary to prepare a mortar sample of a certain size, and after placing it in an environment with relative humidity below 50% for some time, measure the drying shrinkage of the sample with precision measuring equipment, and then calculate the drying shrinkage rate.

Stability Shrinkage Test

The stability shrinkage test refers to measuring the shrinkage of mortar over a long period under fixed temperature and humidity conditions. This test method more accurately predicts the shrinkage properties of mortar. During the test, it is necessary to prepare a mortar sample of a certain size, and after placing it under a fixed temperature and humidity condition for a certain period, measure the shrinkage of the sample through precision measuring equipment, to calculate the stable shrinkage rate.

The method of controlling the shrinkage of mortar

Control the amount of cement

Cement is one of the main causes of shrinkage in mortar. Therefore, in the process of mortar preparation, the amount of cement can be appropriately reduced, thereby reducing the shrinkage of the mortar.

Use high-performance cement

The hydration rate of high-performance cement is slower, which can reduce the shrinkage caused by cement hydration. Therefore, in the process of mortar preparation, high-performance cement can be used to reduce the shrinkage of mortar.

Control cement mortar ratio

The cement-mortar ratio refers to the weight ratio of cement to sand. When the cement mortar ratio is too large, the mortar will be too dry, causing excessive shrinkage. Therefore, in the process of mortar preparation, the cement-mortar ratio should be properly controlled to avoid excessive shrinkage.

Use a shrinkage control agent

A shrinkage control agent is an additive that can control the shrinkage of mortar. The shrinkage control agent can form microscopic holes in the mortar, thereby alleviating the shrinkage of the mortar. Therefore, if it is necessary to control the shrinkage of the mortar, an appropriate amount of shrinkage control agent can be added to the mortar.

Appropriately increase the aggregate

The addition of aggregate can reduce the amount of cement, thereby reducing the shrinkage of the mortar. In addition, appropriately increasing the aggregate can increase the stability of the mortar, thereby further controlling the shrinkage of the mortar.

Keep moist

Keeping the mortar moist will reduce the shrinkage of the mortar. Therefore, during the mortar construction process, the mortar should be kept as wet as possible to avoid excessive shrinkage of the mortar due to drying.

Control the construction environment

The temperature and humidity of the construction environment have a great influence on the shrinkage of mortar. Therefore, during the mortar construction process, the temperature and humidity of the construction environment should be controlled as much as possible to avoid excessive shrinkage of the mortar due to the influence of the environment.

Mortar shrinkage is a common problem in mortar engineering. If it is not controlled, it will hurt the quality and service life of the project. This paper introduces the reasons and testing methods of mortar shrinkage and summarizes the methods of controlling mortar shrinkage, including controlling the amount of cement, using high-performance cement, controlling the cement-mortar ratio, using shrinkage-controlling agents, appropriately increasing aggregate, keeping wet and Controlling the construction environment, etc. By taking these control measures, the shrinkage of mortar can be effectively controlled to ensure project quality and service life.

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