What Is Masonry Mortar?
Masonry mortar refers to mortar that is made of bricks, stones, blocks and other blocks into masonry. It plays the role of bonding, cushioning and force transmission, and is an important part of masonry. Cement mortar is suitable for masonry in wet environment and high strength requirements.
Masonry mortar
1.
basic requirements
1. The workability of the mortar mix should meet the construction requirements, and the bulk density of the fresh mix mortar: the cement mortar should not be less than 1900 kg / m3; the mixed mortar should not be less than 1800 kg / m3. The mix ratio of masonry mortar is generally found in the construction manual or based on experience.
2. The strength and durability of masonry mortar shall meet the design requirements;
3. It should be economically reasonable, and the amount of cement and admixture should be small.
Masonry mortar mix ratio design
1.Calculation of mix ratio of cement mixed mortar
Standard deviation of mortar strength and k (JGJ / T 98-2010) | strength level | Standard deviation of strength (MPa) | k |
Construction level | M5 | M7.5 | M10 | M15 | M20 | M25 | M30 |
excellent | 1.00 | 1.50 | 2.00 | 3.00 | 4.00 | 5.00 | 6.00 | 1.15 |
general | 1.25 | 1.88 | 2.50 | 3.75 | 5.00 | 6.25 | 7.50 | 1.20 |
Worse | 1.50 | 2.25 | 3.00 | 4.50 | 6.00 | 7.50 | 9.00 | 1.25 |
2.Cement mortar mix ratio selection
Amount of cement mortar material per cubic meter (kg / m3) strength level | cement | sand | Water consumption |
M5 | 200 230 | Bulk density value of sand | 270 330 |
M7.5 | 230 260 |
M10 | 260 290 |
M15 | 290 330 |
| M20 | 340 400 |
| M25 | 360 410 |
| M30 | 430 480 |
3. Matching test, adjustment and determination
The materials used in the project shall be used in the trial fitting. The mixing time of cement mortar and mixed mortar is 120s; the mixing time of mortar mixed with fly ash or admixture is 180s. Perform trial mixing according to the calculated mixing ratio, and determine the degree of penetration and delamination of the mixture. If the requirements cannot be met, the amount of materials should be adjusted until the requirements are met; the resulting mixing ratio is the reference mixing ratio.
When testing the strength of mortar, at least three different mix ratios should be adopted, one of which is the benchmark mix ratio, and the other two mix ratios of the cement amount are increased and decreased by 10% respectively compared with the benchmark mix ratio. Under the conditions, the amount of water or admixture can be adjusted accordingly. The three groups of mixing ratios are molding, curing, and measuring the 28-day mortar strength. From this, the mixing ratio that meets the requirements of the trial strength and has the lowest amount of cement is determined as the mortar mixing ratio.
After the mortar mix ratio is determined, when the raw materials are changed, the mix ratio must be determined again through tests. [1]
Including the mortar mix ratio, the consistency of the mortar, the water retention of the mortar, the layering of the mortar and the strength grade of the mortar. Mortar mix ratiorefers to the ratio between the components of the mortar according to the strength level of the mortar and other performance requirements. Expressed in weight ratio or volume ratio. Mortar consistency-refers to the flow properties of freshly mixed mortar under its own weight or external force. Expressed as a standard cone sinking freely into the mortar. Mortar water retention-refers to the ability of freshly mixed mortar to keep the moisture in each layer of mortar uniform during storage, transportation and use, measured by the layering of the mortar. Mortar layering-refers to the difference between the consistency of the freshly mixed mortar and the consistency of the lower mortar measured after the same batch of mortar has been stored for a specified period of time. The strength grade of mortarrefers to a set of 3 pieces using standard test pieces (cubes of 70.7 × 70.7 × 70.7mm), which is cured for 28 days by the standard method, and the average value of compressive strength (MPa) is determined by the standard method. Masonry mortar can be divided into M30, M25, M20, M15, M10, M7.5 and M5.0 according to the compressive strength. The strength of the mortar is not only affected by the composition and proportion of the mortar itself, but also related to the water absorption of the masonry base.
Masonry mortar should be mixed with a mortar mixer. The mortar mixer can be used in the valve discharge type, tipping discharge type or vertical type, and its discharge capacity is usually 200L.
From the completion of feeding, the stirring time should meet the following requirements:
1. Cement mortar and cement mixed mortar shall not be less than 2 minutes.
2. Cement fly ash mortar and mortar with admixture shall not be less than 3 minutes.
3. Mortar with organic plasticizer should be 3-5 minutes.
To mix cement mortar, sand and cement should be mixed evenly before mixing with water.
To mix cement and mortar, dry the sand with the cement evenly, then add the additives (lime paste, clay paste) and water to mix well.
When mixing admixtures, the admixtures should first be dissolved in water at the specified concentration, and the admixture solution should be added when the mixing water is put in. The admixtures should not be directly put into the mixed mortar.
After the mortar is mixed and used, it should be contained in the ash container. If the mortar is bleeding, it should be mixed again before masonry.
The mortar should be used with mixing. Cement mortar and cement mixed mortar must be used within 3 hours and 4 hours after mixing; when the maximum temperature during construction exceeds 30 degrees, they must be used within 2 hours and 3 hours after mixing. For mortar mixed with retarder, its use time can be extended according to specific conditions.
When the strength of masonry mortar test blocks is accepted, the strength qualification standards must meet the following requirements:
The average compressive strength of the mortar block of the same acceptance batch must be greater than or equal to the cube compressive strength corresponding to the design strength grade; the minimum set of average values of the compressive strength of the mortar block of the same acceptance batch must be greater than or equal to the corresponding design strength The cubic compressive strength is 0.75 times.
Note: In the acceptance batch of masonry mortar, the mortar test blocks of the same type and strength level should be no less than 3 groups. When there is only one group of test blocks in the same acceptance batch, the average compressive strength of the group must be greater than or It is equal to the compressive strength of the cube corresponding to the design strength level. The strength of the mortar should be based on the standard curing and compression test structure of the test block with an age of 28 days.
Sampling quantity: Each type of masonry and its strength level of masonry mortar for each inspection batch and not exceeding 250m3, each mixer shall be sampled at least once.
Inspection method: Take a sample at the outlet of the mortar mixer to make mortar test blocks (only one set of test blocks should be made for the same mortar), and finally check the test report of the test block strength.
When the following situations occur during construction or acceptance, on-site inspection methods can be used to test the strength of mortar and masonry in situ or sampling, and determine their strength:
The mortar test blocks are not representative or the number of test blocks is insufficient;
Doubt or dispute about the experimental results of mortar blocks;
The test results of the mortar test blocks cannot meet the design requirements. [1]
