Material Properties for Seismic Testing: Sand

Requested Research

  • Literature review on the influence of sand quality in mixtures for mortars and concretes, with a particular focus on particle size and contaminations.
  • Main request 1. Determination of the key material properties of sand, that may be of influence on the strength development of mortars or concrete elements, as well as the determination of an optimum sand distribution within these mixes.
  • Main request 2. Determination of suitable lab testing methods for obtaining the necessary material properties, including actual testing of specimens. Both main requests are preferably done in collaboration with Structural and Earthquake Engineering.
  • Develop tools and machines for on-site testing of material properties of sand in rural and remote areas. Preferably with Mechanical and Product Engineering.

Status of Research

This is a KEY assignment within the overall SMARTnet project, where all disciplines come together. Open for students and professionals of Architecture and Material Science, as well as for Mechanical and Product Engineering, as well as for Structural and Earthquake Engineering. For more info please contact Martijn Schildkamp at info@smartshelterresearch.com or see our website www.smartshelterresearch.com

Background: Material Properties of Non-Engineered Techniques

The knowledge of how conventional techniques behave in earthquakes is quite high and such techniques have been tested thoroughly. Brick masonry walls and concrete structures can be calculated because the material properties are well known. We can even make quite elaborate computer models of such engineered structures.

This is not the case for most traditional, natural and alternative materials. It is very difficult to model or calculate techniques like stone masonry or earthen structures, due to a high ratio of uncertainties and variables such as material inconsistency and local workmanship. Somehow, these variables must be taken into account.

Background: Rubble Stone Masonry

Our focus is on rubble stone masonry as it is still widely used in the Himalayan areas, which consists of field stones and mortar, which (in the case of cement mortar) is a combination of cement, sand and water. If we incorporate reinforced concrete bands into the walls, we must also add aggregates and reinforcement steel to the list of materials.

This particular research is focusing on each of these materials separately and aims to gain better understanding of the material properties of stones, cement, sand, water, aggregates and steel bars, by investigating the effects of this particular element within their combined actions into mortars, concretes or masonry.

Material: Construction Sand

In the Himalayas, sand is formed by weathering such as freezing and thawing, and by wind, water and gravity erosion of the mountainous rock. The particles are transported by the rivers and deposited on the banks, where it is harvested for use in construction. For instance, in Kaski District of Nepal, the sand mainly comes from two rivers. Seti Khola is known for rough quality sand that is coarse and very suitable for construction purposes (left picture). Madi Khola, on the other hand, has very fine sand, which we recommend for plastering purposes only. The main question of this research assignment is to determine the effect of the particle size of sand in construction elements. Does (too) fine sand indeed have a negative impact on the strength development of mortar and concrete, or are these effects minimal? And can we determine the optimum particle size and particle distribution for different technical applications?

Another topic of interest is the effect of the geological composition of the sand particles themselves. During extensive soil tests by SMARTnet, it was noticed that the soils contain rock particles that are very soft, as a result from the fact that the Himalayas is a relatively young mountain range that is in a constant state of erosion. The picture on the next page shows a sand sample that contains bits of gravel that can be easily crumbled between the fingers, and therefore the overall sample may not contribute sufficiently to the compression strength of a mortar or concrete member.
If the mountain soils contain soft stone particles, it is assumed that the sand deposits near rivers contain such unfavourable particles as well. This assumption must be examined and checked.

The shiny particles on the right picture are possibly mica, which may represent an equal problem for the strength development. This also needs to be validated, for which a literature review is the first step. An important question is how we can simply recognize such potentially harmful particles, in case we want to approve or reject a batch of sand on the building site.

Another point of concern is contaminations in the sand. For instance, the picture below shows a pile of sand that contains a high rate of clay particles. This was easily detected by a simple shake test, but we need to know more about the possible effects of soil contents and organic matter, that may be present in a batch of sand.

Testing of Construction Sand

In order to determine certain mechanical properties of the sand, it is important to interact with the disciplines of structural and earthquake engineering, to understand which properties are needed for their calculations and models. For testing of materials, standard test procedures exist such as ASTM, RILEM or Indian Standards. Part of the literature review is to create an overview of suitable tests and to describe in detail which steps must be undertaken to create consistent test outputs. During the actual testing of samples and specimens, all parameters must remain constant, with the only variable being the sand. That is, the quality of the sand, not the amount of sand in the mix.

Furtherly, this research assignment aims to develop field tests that can simulate the highly controlled lab testing. The challenge is to develop low-tech test procedures and methodologies by using low-cost testing equipment, that is locally applicable in the field, but with reliable test outcomes. This will enable the researchers to conduct simple tests in the field, and it helps the homeowners and masons to buy high-quality products and to use the correct materials.

Ideally this includes simple methodologies and devices that are useful for the workers on-site, such as improved sieving methods and recognition tools for contaminations or unwanted particles.

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