Overview of Flow of Cement Mortar in Cement Testing
Introduction:
Cement mortars play a crucial role in construction as they serve as binding agents for various building materials. The flow of cement mortar is an important property that determines its workability and ease of application. In cement testing, the flow of mortar is evaluated using a flow table test, which provides valuable insights into the behavior of the mortar mixture. This article aims to provide a comprehensive overview of the flow of cement mortar in cement testing, covering key terms and concepts related to the flow table test, cement mortars, and associated testing methods.
1. Cement Mortars:
Cement mortars are mixtures of cement, sand, and water used for various construction applications. These mixtures are typically composed of hydraulic cement, such as Portland cement, masonry cement, or normal concrete, which provides binding properties and strength to the mortar. The proportion of cement, sand, and water, along with the water-cement ratio, significantly influence the flow characteristics of the mortar.
2. Flow Table Test:
The flow table test is a commonly used method to determine the flow of cement mortars. It involves the use of a flow table, a motorized device that provides rotational motion to a flat circular platform. During the test, a test specimen of the cement mortar is placed on the flow table, and the platform is rotated at a specified speed. The flow value, which indicates the diameter of the mortar spread, is measured after a certain number of rotations.
3. Test Procedure:
To conduct the flow table test, a test specimen is prepared by thoroughly mixing the cement, sand, and all the mixing water in a mixing bowl. The water required for the mortar is determined based on the desired water-cement ratio. The mixing operation should be carried out for a specific duration to ensure proper blending of the ingredients. Once the mortar is mixed, it is placed on the flow table in a pedestal form and compacted using a tamping rod. The motorized flow table is then set at a specified speed, such as medium speed or slow speed, and rotated for a designated time period, typically one minute. After the rotation, the flow value is measured by sawing the mortar in a motion perpendicular to the direction of flow.
4. Flow Value and Workability:
The flow value obtained from the flow table test provides an indication of the workability and consistency of the cement mortar. A higher flow value indicates a more fluid and workable mortar, while a lower value suggests a stiffer and less workable mixture. The flow value is influenced by factors such as the water-cement ratio, type and quantity of sand, and the presence of admixtures.
5. Compressive Strength Test and Drying Shrinkage Test:
In addition to the flow table test, cement mortars undergo various other tests to evaluate their performance. The compressive strength test measures the mortar's ability to withstand applied loads and is conducted using standardized procedures, such as ASTM C1437. The drying shrinkage test assesses the dimensional changes in the mortar due to moisture loss, providing insights into the mortar's stability and durability.
6. Mixing Water and Water-Cement Ratio:
The amount of water added during the mixing process significantly affects the flow and workability of cement mortars. The water-cement ratio, which represents the ratio of the weight of water to the weight of cement in the mixture, is a critical parameter in determining the mortar's properties. The water-cement ratio should be carefully controlled to achieve the desired flow value while maintaining sufficient strength and durability.
7. Mixing Process and Equipment:
The mixing of cement mortars can be performed using various methods and equipment. Mechanical mixers, such as paddle mixers or mortar mixers, are commonly used to ensure uniform blending of the ingredients. The mixing process involves adding the cement, sand, and water in specific quantities to the mixing bowl and mixing them until a homogeneous mixture is obtained. The mixing time and speed should be consistent to produce reliable and repeatable results.
8. Test Specimens and Samples:
During the flow table test, test specimens of cement mortars are prepared and tested to determine their flow values. These specimens are typically prepared in batches, and the mortar is poured in layers into a mould. Each layer is compacted using a tamping rod to eliminate air voids and ensure uniform distribution. The number of layers and the extent of compaction may be limited based on specific standards or requirements.
9. Significance and Interpretation of Results:
The flow value obtained from the flow table test provides valuable information about the workability and consistency of cement mortars. It serves as an important parameter for quality control and material assessment. The results can be compared against specified flow value requirements or standards to determine if the mortar meets the desired criteria. Deviations from the specified flow value may indicate the need for adjustments in the mix proportions or further testing.
Conclusion:
The flow of cement mortar is a critical property that impacts its workability and application in construction. The flow table test serves as a standardized method to assess the flow characteristics of cement mortars. By understanding the key terms and concepts related to cement testing, flow table tests, and the properties of cement mortars, professionals can ensure consistent and reliable results in their assessment of mortar workability, strength, and durability.
