Tips From The Pros

BASICS OF SAND: PART 1 - IN THE LAB AND SHOP

Sand is really amazing stuff. It has some interesting physical and chemical properties that are only recently being understood. In sports field management, we use sand in a variety of ways but mainly as a high-performance soil on natural grass sports fields.

The details of sand in an athletic field sense are vast, one could write a book on the subject. Rather than an exhaustive technical discussion beyond the scope here, I’ll focus on some of the basic principles for success based on my experiences. In Part 1, I’ll discuss some of the more important concepts in selecting a sports field sand. In next month’s October issue of Tips from the Pros, I’ll take it out to the field with some practical tips using sand in your operation in Part 2.

First a little nomenclature. Sand is one of three basic soil separates used to define the soil’s texture. Soils can be broken down into groups based on the sizes of the mineral particles. (Get particles sizes). The smallest particles are clay at > .005 mm. Particles sized between .005 and .05 mm are considered silt particles. Sand, in agronomic terms, is defined as those particles between .05 and 2.0 mm. Particles in the soil larger than 2.0 mm are defined as gravel. Based on the percentages (by weight) a soil sample has of these three particles (sand, silt and clay) we group soils into textural classes. See a soil textural classification “triangle” here. As you can see, in order for a soil to be considered a “sand”, it must have at least 90% of its particles in the size range of sand.

Sand particles are further classified into size ranges. For example, sand particles between .50 to 1.0 mm in diameter are considered in the range of “medium sand”. You can see a full range of particle size nomenclature here. In both the USGA and ASTM guidelines, a mix of different particle size ranges is preferred over a sand with uniform particle size. The smaller sand particles pack into some of the larger pores between larger particles largely to give the soil more stability from a physical standpoint. There are also water hydraulics issues involved with the mix of size ranges. The distribution of particle size ranges in the sand soil is the basis of both guidelines, but not the whole story.

Imagine filling a room solely with large beach balls. You would see rather large spaces between the stacked, rounded balls after you have filled the room. In a sand soil, these spaces represent what are called pore spaces. Large pore spaces (macro-pores) in a soil allow water to move (or drain) quickly down through the soil profile. This gravity-powered process goes on even when the soil is saturated, in theory. But in a soil supporting turfgrass plants, we don’t want the water to move out entirely, just the excess water. We want to keep some behind for plant use. Specifying a range of particle sizes is our way of trying to balance the needs of the soil to both drain excess water quickly and keep some for plant health, as well as improving the soil stability for sports play.

In any sand soil, it is important to get the correct size-range percentages of the sand particles as well as other physical and performance characteristics just right to ensure the field will perform as expected. Agronomists have studied the issue extensively and have developed widely used sets of principles and guidelines to help us steer through the details. Do not make up your own sand rootzone specs, hire a qualified professional and/or stay within one of the widely accepted guidelines discussed below. There can be a fine line between success and failure in engineering your sand-based rootzone. Something as seemingly obscure as coefficient of uniformity (see below) of the sand mix can make or break the field. A qualified professional can tailor these guidelines, within the fairly large ranges specified in them on some parameters, to meet the specific needs of your field, the sports played and its location (climate).

Quality Control Program. A professional agronomist with expertise in sports field sands can also design the critical quality control program to ensure you get what you specify in your field from a supplier. A good, written quality control (QC) program is essential to success. Among other items, a good QC program will define the tests to be conducted and the acceptable ranges and thresholds to be used for “Acceptable” or “Rejected”. The accepted protocols used for sampling and testing are described. The sampling/testing intervals and schedule is also laid out. Like any investigation, the chain of custody of samples is considered and defined. The fees associated with expert advice on sand based rootzone construction are nominal compared to the cost of the project and especially the cost of failure. Make sure your QC program is in sync with your overall facility or construction project QC programs and policies.

Guidelines.

While using “pure” sands as root-zones for high-performance golf greens has been around for a while, use in sports field construction really began taking off in the early 1980’s. First-generation artificial turf fields had been gaining in popularity throughout the 70’s. The old, muddy games on native soil fields would begin to close out and sand-based athletic fields took off.

The vast majority of these fields were constructed using the United States Golf Association’s (USGA) guidelines for sand-based golf green construction (see here). There really was no other set of widely accepted guidelines in the US available until 2011 when ASTM International developed ASTM F 2396 Standard Guide for Construction of High Performance Sand-Based Rootzones for Athletic Fields (see here). These guidelines can be purchased online and downloaded, from the ASTM website, for $51.00

The ASTM guidelines generally involves a more coarse range of sand particle size distribution than the USGA guidelines do. Many sports field managers prefer this more coarse sand for construction and maintenance of sports fields. As I understand it, the USGA guidelines were developed for golf greens where the grasses are mowed very short. The generally finer particle sizes may work their way down into the short, tight canopy of a green easier than more coarse sand particles. The golf course superintendent does not want the topdressed sand sitting on top of the green, dulling the mower blades and upsetting the players. On sports fields mowing heights are taller, and a more coarse sand may allow us to take advantage of some of the larger pore spaces and other characteristics prized by sports turf managers everywhere.

As you begin to dig into these guidelines, you will encounter some basic areas of focus. Most field managers drill right into particle size distribution of the sand, and that is important. However, this is only part of the story and only looking at size range distribution in a sports field sand may lead to failure. The first thing to remember about using either set of guidelines is that they are quite general. Many different sands may fit into the specified ranges but perform very differently in the field.

Do it yourself sand particle size distribution.

To determine the particle size distribution of a sand sample, first start with getting a good, representative sample of the sand. This should start out at your sand/root-zone supplier by sampling and testing piles of processed sand destined for your field. Use a long, cut piece of PVC irrigation pipe (or equal) pushed into the pile to get several samples mixed together out of the pile.

You don’t want to just hand-dig the samples off the top of the sand pile. Wind, rain and other natural forces may tend to segregate a thin layer of more-coarse sand particles on the outer edges of the stocked sand pile. Pushing the PVC pipe into the pile a few feet eliminates this bias. I even like to hand dig a small spot a couple inches deep before I plunge in the sample-collecting PVC pipe. I figure this eliminates more bias from the surface of the stockpiled sand.

The next step is to correctly reduce the size of your collected sand sample. It is time consuming to run a sand sample through a set of sieves and weigh them out, so best to make the sample smaller, by splitting it down. But you can’t just pour or separate the sample by hand as different particles sized sand grains will roll and flow differently as you “pour” a sand sample. To avoid this, a contraption called a sample splitter is used to accurately reduce the size of your sample There are many companies selling sample splitters, here is an example of a simple, effective sample splitter.

Sieves. Sand sieves are typically metal, stackable, rounded trays with bottoms made of screen sized to fit the various sizes in your specifications. The sieves are arranged with largest screens on top and sequentially smaller sieves, at the landmark points in your specification (e.g. USGA, ASTM). At the bottom of the stack is a pan to collect the finest particles. You can purchase a set of sand (and gravel) sieves here. The sand sample must be fully dried before splitting and sieve testing. The particles have to flow freely, without water adhesion/cohesion interfering in order to get accurate results in both splitting down your sample and running sieve tests. Your sand sample, now dry and properly reduced to a workable size by the splitter, is poured into the top sieve. The entire stack is then mechanically agitated and each sieve traps sand particles larger than its size. After a few minutes in the shaker, the sand on each sieve size is weighed and calculated as a percentage of the weight of the entire sample. Now you can determine if your sand sample falls into the specified rages of particle size distribution for the guideline you are following.

Percent retained vs percent passing. This part can be confusing, but it’s important to know the difference. After shaking your sieve samples, you can easily weigh and calculate the percentage retained on each sieve to see if it passes against the guidelines you are using. However, some of the more important parameters of a successful sand are determined using a sand gradation curve in which the values are opposite. A sand gradation curve is a graph of the percentages of the sample passing the various sieve sizes, not retained on them.

Think of a do-it-yourself sieve test as a red-flag type of indicator, not as the end-all be-all of your sand based root-zone design. Make important decisions based off analysis at a certified laboratory as part of your written quality control program.

Turf Tips 101: Other Sand Characteristics

Coefficient of Uniformity. The ASTM guidelines specify a range of acceptable coefficients of uniformity. In my opinion, this is often overlooked in sand based sports field rootzone engineering. Essentially, it is a measure of how uniform in size the sand particles within your sample are. ASTM defines this coefficient of uniformity as D60/D10, or the diameter on the sand gradation curve where 60% of the sample passed divided by the diameter where 10% of the sample passed. (See above discussing percent passed vs percent retained). ASTM specifies a coefficient of uniformity acceptable range of 2.5 to 4.5. (Note that a higher CU means less uniform in particle size)

Sand Shape. Sand particle shapes are classified by angularity and sphericity. Generally these come into play in the stability and shear resistance of the sand. A more rounded sand (high sphericity and low angularity) like some wind-blown dune sands, have less particle interlock and may slide over each other like ball bearings. Avoid the extremes in each parameter.

Consider the source. Sand defines a particle size range of different minerals. The parent material can be from several different sources. Calcareous sands are often avoided due to concerns with the potential to slowly ‘dissolve’ over time with some water sources. There is a lab test to determine the calcium carbonate equivalent of your sand and ASTM has guidelines on acceptable levels. Quartz is the preferred parent material due to its durability against weathering (mechanical and/or chemical) over time compared to others like granite.

Note that serious health hazards have been associated with respirable crystalline silica. Crystalline silica is a basic component of many sands, including Quartz sands, along with other naturally occurring materials. The types of materials used and the way they are used in the workplace is important to the associated hazards, from my understanding. OSHA has a good fact sheet on the issue here. According to this OSHA memo from April 2017, the new regulations established March 2016 will begin to be enforced this month, September 2017.

Performance tests. Most important is how your final rootzone mix performs. In fact, ASTM guidelines state “The physical performance criteria should be given priority over sand size distribution specifications.” This makes sense to me. Kind of like how stats are important to an athlete, but wins and losses are more important. Performance tests are conducted using final rootzone material, not just the sand component. So if your design includes organic or inorganic amendments, the final proposed rootzone mix should be tested. Performance tests may include physical tests, chemical tests, and mechanical tests.

Physical tests. These typically include saturated hydraulic conductivity, also referred to as KSat. Think permeability or how well water moves downward through a profile of rootzone mix once the sample has been saturated. The idea is how well will this rootzone drain during prolonged rain events. Keep in mind that after you have built the field and established a mature stand of grass in the rootzone, the KSat values will be significantly lower than the clean rootzone only sample in the lab. Then traffic the grass field and you’ll lower your perc rates more. Other physical tests done in a certified lab may include air-filled porosity, water retention and bulk density. Physical tests are also performed to determine total porosity, air-filled porosity, capillary porosity, and bulk density.

Chemical tests. These may include the calcium carbonate equivalent tests discussed earlier, a traditional soil nutrient test including pH, salinity/sodium levels and percent organic material.

Mechanical tests. These may include the coefficient of uniformity discussed earlier as well as certain shear resistance and load-bearing tests. These are associated with the stability of the rootzone.

A word about rootzone stability. Ultimately, adequate stability of the grass playing surface is what you are after as well as resistance to rutting etc. for heavy load-bearing non-sporting events like concerts. I believe that while we can characterize and compare the certain lab tests related to sand/rootzone stability, it is the grass component (roots and shoots) that are most important to surface stability of the playing field. Different soils of all kinds, including sands, will have variable stability test results, but none of them, without a good grass component, would be stable enough for play as a bare soil field. So while these mechanical tests are important, they don’t completely translate to the surface stability or “footing” on the finished grass field, in my opinion.

Resources of the Month

Did you know there is a world-wide shortage of sand? There is even a thriving black market for sand.

One who collects sands is called an arenophile. There is even an International Sand Collectors Society with a SandFest Conference and everything.

Because of its unique physical properties, sand has been used as a medium for art for centuries. Sand sculpture art can be truly amazing.

Have you ever played with kinetic sand? It can be relaxing and fun.

End Quote:

“Even castles made of sand, fall into the sea, eventually.” – Jimi Hendrix