Hot Mix Asphalt (HMA) is one of the most common roadway materials used today. HMA is a versatile and essential building material that has been used to surface ninety-four percent of the more than 2 million miles of paved roads and highways in the U.S. It is also commonly used to surface parking lots, bike paths and tennis courts.
Typically, asphalt is placed in three distinct layers to create a flexible pavement structure. These layers consist of a base course, an intermediate or binder course, and a surface or wearing course. These layers vary in thicknesses of 3”-6” for base mix, 2”-4” for intermediate mix and 1”-2” for surface mix.
The components of HMA consist of ninety-four percent aggregate and 6 percent asphalt cement a petroleum based product, to serve as the binder. The ingredients are then metered, mixed and brought up to a temperature in excess of 300 degrees Fahrenheit before being placed in a truck and delivered to the jobsite for final placement.
Asphalt pavement is 100 percent recyclable and reusable and is the most reused and recycled pavement material in the U.S. Reclaimed Asphalt Pavement (RAP) can be incorporated into the new pavement at replacement rates in excess of thirty percent depending upon the mix and the application of the product.
The use of Warm Mix Asphalt (WMA) or “green” asphalt is becoming increasingly popular. The immediate benefit to producing WMA is the reduction in energy consumption required by burning fuels to heat traditional hot mix asphalt (HMA) to temperatures in excess of 300° F at the production plant. These high production temperatures are needed to allow the asphalt binder to become viscous enough to completely coat the aggregate in the HMA, have good workability during laying and compaction, and durability during traffic exposure. WMA can reduce the temperature by 50 to 100 degrees Fahrenheit. With the decreased production temperature comes the additional benefit of reduced emissions from burning fuels, fumes, and odors generated at the plant and the paving site.
Asphalt consumption in the U.S. is of between 500 to 550 million tons per year and is produced out of over 4,000 asphalt plants with a total value in excess of $30 billion.
Aggregates, paramount to the development of the world economy, are construction materials consisting of crushed stone, sand and gravel. Construction aggregates are core to Summit Materials business strategy as they are key material components used in the production of asphalt, concrete, and cement, and are used for highway, commercial and residential construction.
Aggregates are generally extracted from the earth using surface or underground mining methods and are produced from natural deposits of various materials such as limestone, sand and gravel, granite and trap rock.
When mixed with a “binder” or “glue”, aggregates are used as a core structural component used to create other materials. With the addition of Portland cement and water, ready- mixed concrete can be produced for use in structures, pavements, bridges, etc… With the addition of liquid asphalt cement, (liquid AC), hot mix asphalt is produced for use in roadways, airport runways and parking lots.
While most of the population may not be familiar with the term “aggregates”, our lives are continuously impacted by them. Whether it is a material used in the construction of housing, hospitals, schools or work space, or as a product used in the construction of roads, bridges and parking lots, we constantly touch aggregates to allow us to perform the functions of our daily lives.
On average, 10 tons of aggregate are required annually for each U.S. citizen, or approximately 3.0 billion tons annually. It requires approximately 38,000 tons to construct a one mile stretch of a typical four-lane interstate highway.
Summit Materials provides civil construction services to both the private and public sectors and work as either a prime or sub-contractor. Our companies perform work that complements our heavy-side construction materials business by providing a downstream outlet to distribute these products through, in addition to the normal external distribution channels.
Our companies perform quality work within the classifications of earth-moving, grading and draining, asphalt and concrete paving, site development, underground pipe installation and other integrated functions required in the infrastructure and highway construction industry.
Our customers benefit from our experienced field supervision and skilled labor force that utilizes quality equipment and materials.
Ready-Mix concrete is the most versatile and widely used material in worldwide construction today. Its flexible recipe characteristics allow for an end product that can assume almost any color, shape, texture and strength to meet the many requirements of end uses that range from bridges, foundations, skyscrapers, pavements, dams, houses, parking garages, water treatment facilities, airports, tunnels and power plants, hospitals and schools. This versatility gives concrete designers a spectrum of unlimited potential.
There are five primary ingredients that constitute a basic concrete mix:
• Coarse Aggregate (CA)
• Fine Aggregate (FA)
The water and cement are combined and a chemical reaction is produced called hydration. This paste or binder represents between 25 to 40 percent of the volume of the mix that coats each particle of aggregate and serves as the agent that binds the aggregates together. The aggregates represent 60 to 75 percent of the mix by volume, with the remaining volume (4% – 8%) consisting of entrapped air that was generated by using air entraining admixtures. Once fully hydrated, the plastic concrete will then harden and take on the shape of the form in which it was placed.
The quality of a concrete mix is generally determined by ratio of water to cement. The water cement ratio is determined by dividing the weight of the water by the weight of the cement. It physically only requires approximately 0.29 lbs of water to hydrate 1.0 lbs of Portland cement; any amount in excess of this is generally used to gain workability. Higher quality concrete is produced by lowering the water-cement ratio as much as possible without sacrificing the workability or finishability of the fresh concrete. Specialty admixtures such as high range water reducers can aid in achieving this condition without sacrificing quality.
Other materials commonly used in the production of ready-mix concrete include fly-ash, a waste byproduct from coal burning power plants, silica fume, a waste byproduct generated from the manufacture of silicon and ferro-silicon metals, and ground granulated blast furnace slag, a byproduct of the iron and steel manufacturing process. All of these products have cemetitious properties that enhance the strength, durability and permeability of the concrete.
The U.S. alone consumes approximately 340 million cubic yards of concrete fueling a $35 billion industry which employs over 2 million workers and covering 55,000 miles of roadways.
Some different types of concrete include Lightweight Concrete, High Performance Concrete, Self Compacting/Consolidating Concrete and Architectural Concrete.
Portland cement is the basic ingredient of concrete. Together, with water, it creates the paste that binds the aggregate together to make concrete. Few construction projects can take place without utilizing Portland cement somewhere in the design, making it a key ingredient used in the nation’s construction industry.
U.S. cement production is distributed among 36 states utilizing 113 production facilities. U.S. cement consumption traditionally outpaces domestic production capacities with the shortfall being supplied with imports.
The majority of all cement shipments are sent to ready-mix concrete operators. The rest are shipped to manufacturers of concrete related products such as block and precast, oil well service companies, contractors and government entities.
The domestic cement industry is regional in nature with customers purchasing material from local sources. Nearly 98% of U.S. cement is shipped to its customers by truck. Barge and rail modes account for the remaining distribution modes. Portland cement consumption or demand is seasonal in nature with nearly two-thirds of the U.S. consumption occurring within a six month period between May and October.
Portland cement is made from common materials such as limestone, shale, clay, silica, and iron ore. The principle raw materials are a blend of 88% limestone, 6% shale, with the remaining raw materials being clay and iron ore. Generally, the limestone and shale are mined from quarries located on site with the production plant. These core ingredients are blended and crushed into a fine grind and then preheated and ultimately introduced into a kiln heated to about 2700 degrees F. Under this extreme heat, a chemical transformation occurs uniting the elements to form a new substance with new physical and chemical characteristics. This new substance is called clinker and it is formed into pieces about the size of marbles. The clinker is then cooled and later ground into a fine power that then is classified as Portland cement.ent.