Masonry Magazine August 1993 Page. 19
Gradation
ASTM C144 limits the amount of material passing the No. 200 sieve to a maximum of 1.0% and the lightweight particles to a maximum of 0.5%. Exceptions to these limits and additional tests that may be used to qualify sands not meeting these limits are outlined in the composition section of ASTM C144.
Soundness
Aggregates can deteriorate when subjected to weathering. ASTM C88, the Standard Test Method for Soundness of Aggregates by use of Sodium Sulfate or Magnesium Sulfate, is used to estimate the soundness of sand subjected to weathering action. ASTM C144 requires that the weight loss of sand tested according to ASTM C88 be a maximum of 10% when sodium sulfate is used or a maximum of 15% when magnesium sulfate is used. Sand not meeting the ASTM C88 test requirement may be used, provided there is a record of that aggregate having given at least five years service in comparable weathering environment without appreciable disintegration.
Alkali-Aggregate Reactivity
There is also the possibility that the sand itself may be chemically reactive with cement or lime, a phenomenon called alkali-aggregate reaction, which may cause abnormal expansion and cracking. Experience records of the sand source usually provide the information needed for the selection of nonreactive aggregates. While ASTM C144 does not address alkali-aggregate reactivity, if a sand is suspected of being chemically unstable and there are no service records, it can be tested for suitability. The American Society for Testing and Materials has several tests and a recommended practice for identifying alkali-reactive aggregates. Appendix X1 of ASTM C33, the Standard Specification for Concrete Aggregates provides additional information on the available tests and their application.
Proper Handling
Proper handling procedures are important to prevent contamination and segregation.
Sand should never be shipped in unclean barges, freight cars, or trucks that have previously carried chemicals or salts that may contaminate the mortar. Such vehicles must be properly cleaned.
Another source of contamination is the use of rusty material-handling equipment. Rust particles in sand can cause unsightly iron stains in mortar joints.
Care must also be taken not to use mortar boxes, wheelbarrows, and shovels that have been used for handling de-icing salts or other chemicals without first thoroughly cleaning such equipment.
Segregation of coarse and fine particles will take place if proper handling methods are not used. Free fall of sand from the high end of a conveyor should not be allowed. Even a gentle wind will separate the fine from the coarse particles and cause different gradations in different portions of the stockpile. Sand should be transported to the job site in a damp loose condition.
Proportioning by Volume
The unit weight of sand is dependent on the surface moisture. Surface moisture on sand particles causes bulking, which is an increase in volume compared to dry compacted sand. Maximum bulking can occur when moisture content is approximately 5%. Thus a cubic foot of damp loose sand typically weighs only 80 lb. A cubic foot of dry sand usually weighs approximately 100 lb. Fine sands bulk more than coarse sands. Fig. 2 shows the relationship between moisture content, sand gradation, and unit weight.
Fig 2. Weight of loose, damp sand.
Since sand used in masonry mortar is generally proportioned by volume, the effect of bulking can be significant to the amount of sand batched with cementitious materials to make mortar. ASTM C270 specification requirements are based on the assumption that sand used in construction is damp and loose, having a surface moisture in the 5% range. Sand should therefore be maintained in a damp loose condition to avoid variations in proportioning. The sand pile at the construction site should be covered to reduce evaporation and provide protection from rain or snow.
Sand is commonly added to the mortar mixer using a shovel. However, some positive control should be established to assure that the proper volume of sand is used. That can be accomplished by periodically checking the required shovel count with a cubic foot box, using a cubic foot measuring box to add the sand to the mixer, or using