Materials Engineering Laboratory
The Materials Engineering Laboratory (Lab) is responsible for and provides materials-related services for City and private development projects.
- Plant inspection, sampling, and laboratory testing of most construction materials (such as aggregates, asphalt, and concrete) prior to use for new or rehabilitated City infrastructure to check that the materials comply with City and/or project specifications/requirements.
- Field and laboratory testing during construction to check that the contractor and their construction methods achieve the specified test results, such as slump and compressive strength of concrete, and the density/relative compaction of soil, aggregates and asphalt.
- Evaluating new and alternative technologies relative to construction materials and methods.
- Pavement Management Program (PMP):
- Street inspections of the pavement distress conditions are performed throughout the year; 25% of residential streets and 50% of the arterial and collector streets are completed annually. Data is currently collected and input into our StreetSaver® PMP using PDA’s.
- Maintaining the database for the City’s street network (~500 centerline miles; replacement value estimated at $1.1billion) allowing us to perform up-to-date planning level analyses such as determining recommendations for cost-effective pavement project selection based on limited pavement funds.
- Pavement Engineering:
- Traffic Index(TI) – determining the TI which quantifies loading on our pavements from various types of vehicles, such as trucks and buses.
- Structural Section – using the TI and subgrade soil strength value, we develop the required pavement structural section for Capital Improvement Projects (CIP).We also review and approve the pavement structural section design for City streets on private development projects.
- Coring and evaluation of new or existing pavement to aid in determining the appropriate pavement rehabilitation treatment and/or to check that the contractor placed the required quality or thickness of asphalt, if warranted.
In 1972 the City Lab designed and built a drill rig, which was hydraulically-powered and mounted in a van. This drill rig provided us the capability of coring asphalt and Portland cement concrete pavement. This van-mounted drill rig was replaced in 2015, when we purchased hitch-mounted coring equipment. The hitch-mounted equipment allows us the flexibility of using the same Lab truck for project nuclear density gauge compaction testing of various materials when we are not needing to core for a project.
Our current coring equipment is gas-powered, and uses a diamond-tipped core barrel to cut through asphalt or concrete pavement surfacing. The core barrel is cooled by water as significant heat is generated during the spinning and cutting action of the core barrel. We currently have core barrels with diameters of 2-, 3-, 4-, 6- and 8-inches. The life of each core barrel depends on frequency of use, while their cost depends on the size and type (i.e., asphalt or concrete core barrel). We generally use each barrel for at least several years, and we spend in the range of $200 to $300 per core barrel.
Pavement core samples are occasionally obtained on newly surfaced streets when there is a are concern about the pavement thickness and/or the properties of the pavement (e.g., density, strength, air voids, etc). The cores are brought back to the Lab, where the appropriate test(s) can be performed on the intact core sample and/or on re-constituted asphalt material after the cores are re-heated in our ovens.
During the design of CIP projects, existing streets are often cored to confirm their structural section. Based on the actual structural section of the streets undergoing rehabilitation, adjustments may be possible to the preliminary design to allow a more cost-effective pavement rehabilitation. An example of this service recently occurred on the Elizabeth Way Water and Sewer Capital Improvement Project. Instead of requiring a rebuild of the street with a typical 0.55’ full-depth asphalt section, we obtained two (2) core samples and determined the actual pavement was thicker than the historical plan reviews indicated. As such, the final pavement rehabilitation will consist of a new 0.37’ thick asphalt surfacing over a minimum of 0.38’ of existing aggregate base for an overall reduction in asphalt tonnage required for this project of ~33%.