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In the lab with Mr. Sandman
“Sand” refers to a type of sediment that is defined by its grain size. In most countries, sand is classified as having a grain size ranging from 0.063 mm to 2 mm. Grains smaller than this are called silt, while larger grains are referred to as gravel. The grains can be composed of a variety of minerals and chemical components. However, by far the largest proportion of sand on our planet consists of quartz grains (silica sand or silicon dioxide). Because silicon is the most common chemical element on earth after oxygen, we have long been under the impression that sand reserves are virtually inexhaustible.
This has changed dramatically. Back in 2014, the United Nations Environment Programme (UNEP) published a report that emphatically pointed out that humanity is consuming too much sand. The new 2022 report already speaks of a real “sand crisis.” This is because sand is not only an important raw material for the construction industry and numerous other industries, but it also plays a strategic role in our ecosystems. All 17 UN Sustainable Development Goals (SDGs) are directly or indirectly linked to sand as a resource.*
Time to zero in on sand
The extraction of river, coastal or marine sand is particularly critical because it directly affects ecosystems. Sand extraction damages biodiversity, increases erosion and weakens the resilience of deltas and coastal areas to the effects of climate change. However, this type of sand is particularly valuable to the construction industry because it has the optimal shape for the formulation of concrete and mortar.
A dilemma? More like a challenge. After all, couldn’t we simply change our formulations so that other aggregates also deliver optimal results? But how “simple” is it? Different teams from our technical competence centers have looked into this question and set out to find regional answers on site. We invite you to join us on this journey towards greater circularity in the construction industry. Stop by and explore our projects with experts based in Burghausen (Germany), Mumbai (India), and soon in Dubai (UAE).
First stop: Burghausen, Germany – a crush on recycled concrete
Since the construction industry not only consumes large amounts of sand, but also produces large quantities of construction waste, it makes sense to use this waste as a raw material. So our team in Burghausen pursued the idea of replacing sand with fine-grained fragments of recycled concrete.
The starting material was recycled concrete from Ettengruber GmbH Recycling und Verwertung, which was crushed to the required size by the Laboratories for Building Materials and Construction Chemistry at the Munich University of Applied Sciences under the direction of Professor Andrea Kustermann.
“We experimented with particles up to 1.25 mm in size and started by looking at the differences between a standard quartz sand and limestone mix and the broken concrete.”
Dr. Klas Sorger, Technical Service Manager, Europe
Another difference was found by testing with a capillary pycnometer according to DIN 18124. The particle density of the recycled concrete was 2.3 and 2.4 g/m3, which was lower than that of the quartz sand at 2.63 g/m3. This suggests a higher number of fine pores with diameters between 10 nanometers and 5 micrometers, which was confirmed by measurements with a mercury injection porosimeter.
“The high proportion of fine particles and fine pores requires an adjustment of the tile adhesive formulation. To achieve the same consistency, the tile adhesive with recycled concrete needs more water during mixing. We also chose the polymer binder accordingly. We decided on VINNAPAS® 8620 E. This dispersible terpolymer powder based on VAE (vinyl acetate-ethylene) and VC (vinyl chloride) improves the wet strength and flexibility of the adhesive.”
Dr. Klas Sorger
Determining open time by measuring tensile adhesion strength. In formulas based on recycled concrete, the tensile adhesion strength was higher after 20 and 30 minutes than was the case for the reference. Open times are therefore extended.
A C2TES1 class tile adhesive in accordance with EN 12004 was used as a reference. In two sample formulations, we replaced 25% and 50% of the silica sand with recycled concrete, and we adjusted the water content accordingly. Standard tests were then conducted on both the fresh mortar and the cured tile adhesive.
“We found no differences in the key properties of the fresh mortar, such as viscosity, consistency and slip resistance. In fact, the sample formulations were superior in terms of wetting capability: the higher the recycled concrete content, the better the wettability. This also means an extended open time, which is particularly advantageous today when large tiles are being laid.”
Dr. Klas Sorger
Study on initial tensile adhesion strength (gray) versus tensile adhesion strength values following water immersion (light blue), heat storage (purple) and freeze-thaw cycles (orange). The results for formulations based on recycled concrete were not significantly different from those for the reference formulation.
It was interesting to see that improved wetting capability and extended open times have no negative impact either on the initial tensile adhesion strength or on tensile adhesion strength following storage in water, at elevated temperatures or under freeze-thaw conditions. According to a team from the Technical University of Lisbon, this is possible because the fine-pored particles of the recycled concrete act as water reservoirs that release water over time.
“We repeated the tests six months later with a different batch of Ettengruber recycled concrete. Fortunately, we were able to reproduce the results of the previous study, indicating that the batches were not significantly different. In practice, this could mean that the formulation only needs to be adapted once to the locally available recycled concrete. This shows a possible way toward more circularity in tile adhesives.”
Dr. Klas SorgerSecond stop: Mumbai, India – building on manufactured sand
According to industry estimates, India’s sand demand reached approximately 1,006 million metric tons in 2023 and is expected to continue growing. At the same time, the environmental impacts of sand mining on river ecosystems, including sediment depletion, bank erosion, and habitat degradation, are fully recognized. Studies show that the sediment load of the Ganges-Brahmaputra delta was halved between 1960 and 2008, from 1 billion tons to 500 million tons per year. This reduction in sediment flow is largely attributed to human activities, such as sand mining.
An alternative to natural river sand is manufactured sand (M-sand). It is produced by crushing rock, quarry stone or larger aggregates into sand-sized particles. This happens in a three-stage process using jaw crushers, cone crushers and vertical shaft impact (VSI) crushers. The result is finely graded crushed stone with a uniform particle size designed to mimic the properties of natural sand used in construction.
“We see sand shortages in India, especially in the southern region. As a result, we have been receiving requests for sand alternatives. The most requested alternative is M-sand.”
Surabhi Jain, Technical Service Manager, IndiaWhen we looked closer at the subject, we found typical differences between river sand and M-sand. The most prominent include:
- Grading and particle size: M-sand can be processed with a specific grain size and distribution. We recommend that the grain size should be similar to that of river sand.
- Shape and texture: Natural sand has a rounder shape and smoother texture than manufactured sand, which tends to have a cubic shape with rough surfaces.
- Moisture content: Moisture is only available in water-washed M-sand. In natural sand, moisture is always present because it is trapped between the particles.
- Concrete strength: Due to their special cubic shape, the manufactured grains interlock easily. In concrete, this results in higher bond strength, compressive strength and modulus.
- Silt content: Manufactured sand has zero silt. For river sand, the minimum permissible silt content is 3% going up to 20%.
- Purity: In addition to being free of silt, M-sand does not contain clay or dust and has a tighter particle packing. The lower number of voids reduces the amount of cement required in concrete production.
“M-sand is primarily used in concrete production as it offers good compressive strength, durability and workability. In tile adhesive formulations, we have seen good bond strength but some challenges with open time and workability.”
Surabhi Jain
As you can see, the adhesive bond strength of the M-sand formulations is at least as good as for the standard formulation. A: after standard conditioning (SC): 28 days, 23 ± 2 °C + 50 ± 5% RH; B: after water immersion: 7 days SC + 21 days water immersion; C: after heat aging: 14 days SC + 14 days at an oven temperature of 70 °C.
At our technical competence center, we have tested various types of manufactured sand in tile adhesive formulations. Our results show that river sand can be replaced up to 100% by M-sand, if the quality is right.
The results shown here were achieved with three formulations: #1 is a standard formulation with 100% quartz sand. In formulation #2, 100% quartz sand was replaced with M-sand, and in formulation #3, 20% was replaced with M-sand. All three tile adhesives were modified with 2% of our neutral, standard dispersible polymer powder VINNAPAS® 5010 N.
Open time is an essential indicator of how long the tiler can embed the tiles into the applied tile adhesive mortar while still meeting a specified tensile adhesion strength. Results show, that open time decreases with the amount of manufactured sand. It is dramatically lower with the formulation with 100% M-sand.
We tested two possibilities to counterbalance the decreased tensile adhesion strength of formulations with M-sand. One: we replaced the neutral VINNAPAS® grade with a more specialized grade. VINNAPAS® 8620 E was specifically developed to increase open time and workability in tile adhesives. Two: we increased water demand in the formulations.
We can already observe the effect of VINNAPAS® 8620 E on open time in the standard formulation. This is even more pronounced in the formulation with 100% M-sand. VINNAPAS® 8620 E more than triples the tensile adhesion strength after 20 minutes.
Recommendations at a glance
As a conclusion of our tests, we recommend that customers who want to replace river sand with manufactured sand to use three levers:
- Choosing M-sand with a similar particle size to river sand
- Choosing the right amount of M-sand
- Counterbalancing negative effects with a suitable dispersible polymer powder
“I am convinced that this is the right way forward. We should not be looking at how we can continue to work with materials that we know have such a high environmental impact. We should be working on how to make high-quality tile adhesives with the materials that are reasonably available to us. I can only invite you to get us started. Because if everyone works closely together, we will get closer to a circular building industry.”
Gustavo Soares, Global Segment Manager for Tile Adhesive Applications
Stay informed!
Our colleagues at the technical competence center in Dubai are currently conducting tests with dune sand in tile adhesive formulations. The results will be published here as soon as the tests have been concluded and reviewed.
If you leave your contact details here, we will send you a notification as soon as the results are online.
Register here
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