16 March 2019
The construction industry has by far the biggest sand footprint in the world, claiming one third of its 40 billion-ton-a-year consumption. With the current surge in construction activity at the global level, and notably in Asia, this consumer trend shows no sign of abating. As a consequence, there is international recognition that natural sand reserves and the eco systems of which they are a crucial regulating element, need to be maintained.
Indeed, primary sources of natural sand, river beds and deserts are now increasingly being protected by governments that closely monitor sand mining and sanction illegal operators. Often, when unable to mine for natural sand, some operators resort to using unwashed crusher fines to produce cement and mortar at low cost, producing poor to very uneven results.
But it is not a case of ‘either - or’, natural sand or unwashed crusher fines. For those who wish to produce sand at consistent quality and quantity levels, with the option to choose specific grades, materials washing is the simple and accessible solution for their operations.
Erosion and product instability through water penetration
Unwashed crusher fines, as a waste material left over from crushed rock, feature a gravel-like surface and are used as trail and car park surfacing as they pack well, as long as subgrade preparation and drainage work has been done. This is on the understanding that the underlying soil is suitable for use of unwashed fines.
However, regardless of the quality of the preparation work, unwashed crusher fines remain vulnerable to wash-outs from rain and all types of running water (streams, melting snow, etc). Their use is also limited to specific construction operations with unsophisticated needs, such as hiking trails. Even then, the texture of crusher fines, which can be too smooth or too hard, can fail to make the grade for a fully accessible surface. Additives such as lime are then used to help to even out the texture, which in turn creates a new set of difficulties in terms of reaching a balance that will never produce an exact, replicable mixture offering consistency in results.
When comparing the physical properties of fine aggregates, figures speak for themselves.
Experts can evidence why using washed sand and aggregates to reduce water penetration makes sense:
A carefully measured combination of cement, sand, gravel (or rock chippings) and water, “concrete is in fact the most used man-made material in the world, with three tons used annually for each man, woman and child. Twice as much concrete is used around the world than the total of all other building materials, including wood, steel, plastic and aluminum. Its superior properties on strength, durability, thermal mass and affordability make it the material of choice for most purposes.
In a nutshell, concrete is the beating heart of the construction industry: it needs to be strong, versatile and of course value-for-money for constructors who want to maintain their competitive edge. All these requirements are interconnected and when each box is ticked, the operator knows that along with their customer they have mutually benefited from using washed sands.
Strength and versatility: the stronger the concrete, the wider scope of applications it will adapt to.
When choosing materials to mix concrete for their operations, construction companies understand that unwashed crushed fines can inhibit the quality of the final product and need to make a choice based on the type of application they have been working towards and priorities such as product longevity and quality.
Choosing unwashed crushed fines often leads to adding more chemical and mixtures to compensate for poor quality sand. As concrete performance directly depends on the quality of the sand used in the mix, more and more construction companies now choose the safe, quality option of washed m-sands that are made to their exact specifications.
It’s a no-brainer: it has been demonstrated that the use of washed m-sand in the mix will greatly increase your concrete’s compressive strength and therefore workability when compared to crusher fines. In the same vein, levels of flexural and split tensile strength when using washed m-sand have shown to jump ahead of levels achieved by crusher fines by up 19%.
Cost: better sand, better, stronger concrete.
Cement is expensive. Indicative of the cost-saving aspect of sand washing, washed concrete sands compare favourably to unwashed crusher fines when looking at the weight required in the mix proportion. It takes 355 kg/cum of crusher dust/fines to catch up with the result only 300 kg/cum of washed sand achieves.
Mortar, a thick mixture of water, sand and cement, cannot be substituted for concrete (and vice versa) at the risk of serious quality failure in the final product. A substance that needs to be replaced every 25 to 50 years, its longevity makes it unsuitable for structural projects. With a higher ratio of water to bond the mixture together, it is used to glue building materials such as bricks. To be value-for-money, mortar needs to stand the test of time.
As with concrete, mortar mix benefits greatly from incorporating washed plaster sand as opposed to unwashed crusher fines. Using washed m-sand not only increases the quality of the mortar but also significantly reduces costs as you need substantially more plaster sand than you would crusher fines to obtain the same quantity of mortar. Typically, it takes 34% less washed m-sand than VSI crusher fines to mix good quality concrete.
The average flexural strength is also improved with washed m-sand, boasting 1.8 N/mm² compared to VSI crusher fines’ 0.89 N/mm². Importantly, when it comes to cracking, testing shows that the crusher fine-mortar ring displays uneven texture and various cracks after just 6 hours, when the washed m-sand-mortar ring retains an even texture and only starts to show light cracks after 48 hours.
Source : cdeasia.com