Technical information
How MRP sands are processed, how to specify them, and what the common tests and terms mean.
One deposit, three processes
Everything MRP supplies comes from a single quartz sand deposit at Talgai, Queensland, and is processed on site. Raw sand is washed to remove silt and clay, screened to a grading, and where a dry or sized product is required, kiln-dried and screened again. Thermal bedding sand is the exception: it is screened and graded but not washed, because the fines are what let it compact. Because the deposit and the plant do not change, the product does not change between deliveries.
Grading and sieve analysis
A sand is described by its particle size distribution: the proportion by mass passing each sieve in a standard set. The result is plotted as a grading curve. Two sands can have the same maximum size and behave completely differently depending on how much of each size is present. A well-graded sand has a spread of sizes and packs densely; a single-sized or uniform sand has most of its mass in one fraction and packs loosely but drains freely. Which is wanted depends entirely on the job — thermal backfill wants the first, filter media wants the second.
Fines
Fines in a natural sand means silt and clay — material finer than 75 micrometres. In concrete, mortar and render they raise water demand and weaken the bond, so fine aggregate is commonly specified with reference to AS 2758.1, which limits them. Washing is how a natural sand is brought within those limits. In thermal backfill and controlled fill the same fines are an asset: they fill the voids between larger grains and let the material compact. This is why MRP washes some products and deliberately does not wash others.
Filter media: effective size and uniformity coefficient
Filter sand is specified by two numbers read off the grading curve. Effective size (D10) is the sieve size that 10% of the sand passes; it governs how fine a particle the bed captures and how quickly head loss builds. Uniformity coefficient (D60/D10) is the ratio of the 60% passing size to the effective size; a low value means a narrow, uniform grading that filters and backwashes evenly. Meeting a specification of this kind requires a sand that has been washed, dried so it can be screened accurately, and screened into a narrow fraction. That is what the kiln-dried range is produced for.
Moisture
Washed sand is supplied moist from the wash plant. Kiln-dried sand is supplied dry from the kiln. Moisture matters in two places: for dry-mix and pre-blended products, where water in the sand would start hydrating the cement in the bag; and for anything that has to flow through a spreader or into a joint. Where a formulation sets a maximum moisture content, state it at the time of enquiry.
Controlled fill and compaction
Fill is specified by the density it must reach when compacted, usually as a percentage of a laboratory maximum dry density determined for that material, with field density testing of each layer. The tests are carried out on site by the project’s geotechnical testing contractor. What the fill supplier controls is consistency: a screened, uniform material compacts the same way every time, so the target density is achievable with a known number of passes. MRP Select Fill is supplied on that basis.
Thermal resistivity
Backfill around a power cable is specified by its thermal resistivity — the resistance it offers to heat flowing away from the conductor. It is measured on a compacted sample at a stated density and moisture content using a thermal needle probe, and the project specification sets the maximum permitted value, often at both the placed moisture and fully dry. The property that drives the result is density: a well-graded sand with its fines retained compacts with few air voids, and air is what resists heat flow. MRP Thermal Bedding Sand is graded for that purpose. Where a specification calls for a measured value, state this at the time of enquiry.
Test results and documentation
MRP Sand Quarry is a Queensland Department of Transport and Main Roads approved producer. Where a project specification requires grading results, test certificates or source registration, state the requirement when you enquire and it will be addressed for the product and quantity in question. Standards named on this site are referred to as the specifications customers commonly work to; they are not claims of certification.