Product Description

Aggregates are commonly known by their different names such as sand, pebbles, gravel, and rocks among others. Aggregate materials are the basic building blocks of concrete. These materials play a major role in the structure of soils and have huge implications on the way we build our environment. Soil aggregate size distribution controls many processes in the soil environment including erosion control, water infiltration rates, pore sizes, and drainage. In addition, aggregate size affects the characteristics of the soil such as its hydraulic conductivity, porosity, bulk density and texture. A big problem with the use of aggregates is that they are often improperly sized and are not properly managed. Improperly sized aggregate results in poor performance, inefficient use of land and increased maintenance costs.

Size Distribution

The United States Department of Agriculture (USDA) recommends that aggregate size distributions should fall between 2mm-10mm. Smaller aggregates are best utilized for topsoils whereas larger ones are suitable for subsoils. Aggregate size distribution also determines how much space is left over for vegetation. As the size of aggregate increases the amount of open space decreases. When planting in rows, it gives the gardener the option of using smaller aggregate than if he was using larger aggregates.

Sizes

There are two types of aggregate materials: natural and manufactured. Natural aggregates are derived from naturally occurring deposits. Manufactured aggregates include crushed stone, sand, expanded shale, and river gravel. Each type of aggregate consists of various shapes and textures. There are different methods to measure aggregate sizes including visual estimate, automated sorting machines, sieve analysis, vibrating screen, and sedimentation method. Visual estimation is the simplest method to determine aggregate size distribution. By visually estimating the size of aggregates, one is able to make rough estimates on the percentage of each particle size present in the mixture.

Mixtures

When mixtures of aggregates are used, care must be taken to ensure that the ratio of each aggregate size is maintained. If the aggregates are not mixed together properly, then the landscape could suffer from segregation and decreased functionality. For example, a mixture of small and large aggregate may cause the larger particles to settle out and occupy a greater portion of the base material than desired. Segregation can also be caused by improper mixing ratios of aggregates. This can lead to uneven distribution of soil nutrients, decrease water uptake, increase compaction, reduce drainage and increase erosion.

Aggregate Size Mixture Design

For optimal utilization of aggregate, proper sizing and mixtures are necessary to avoid problems associated with segregation. Using large amounts of small aggregates or small amounts of large aggregates will result in improper size distribution of the soil and thus reduced functionality. To prevent segregation, it is recommended to carefully mix the aggregates before adding them to the base material. Before adding the mixtures to the base material, it is recommended to thoroughly mix the aggregate and add it in layers. Once the layer is dry, continue the process until all the layers are dry. Adding the mixture to the base material at least two weeks prior to planting ensures that the roots of the plants do not have time to pull down any loose aggregate particles. Another thing to consider before applying the soil mixture is the size of the aggregate and the depth of the hole. Mixing aggregates that are too large or small will alter the balance of the soil mixture and may affect the root system of the plant.

Using the wrong mixture of aggregate will result in poor quality topsoil and increased maintenance costs. Therefore, it is critical to get the correct mixture of aggregate and apply it at the right time. Since it takes months for a mature plant to start producing fruits, it is advisable to wait until the plant starts flowering before applying the mixture.