The David Dixon Memorial Materials Laboratory is responsible geotechnical engineering, engineering geology, and pavement analysis as well as acceptance testing and quality assurance of construction materials for capital project programs, maintenance programs, and development activities for the County of Orange and other eligible agencies that request the County’s assistance.
The Materials Laboratory provides the following services:
- Geotechnical and foundation investigation with related requirements for all public works facilities (including building foundations)
- Soils evaluation and pavement design for all public and private streets, including:
- Asphalt concrete mix designs
- Portland cement concrete mix designs
- Soil stabilizing mix designs
- Quality assurance testing on construction materials including Portland Cement Concrete, soils and asphalt concrete for all County projects, subdivision infrastructure, County property encroachment permits, flood control projects and eligible outside agencies
- Evaluation of testers (County staff and staff of consultant laboratories) to verify procedures and correct performance of test methods and their test equipment for compliance with project specifications
Geotechnical Investigation & Pavement Design
The Materials Lab performs site specific geotechnical investigation to prepare geotechnical reports and materials reports for infrastructure projects. The preliminary geotechnical investigation involves drilling deep and shallow exploratory borings, soils sampling, laboratory testing, engineering analyses and preparation of reports. Reports may include geotechnical recommendations for bedding material, trench backfill, compaction requirements, soil corrosivity, bearing capacity, requirements for temporary and permanent slopes, shoring recommendations, grading for slope repair, concrete pipe design, seismic parameters, construction considerations, and other special provisions.
The Materials Lab also performs petrographic analysis of construction material and Ground Penetrating Radar (GPR) survey for forensic geotechnical investigation.
The Materials Lab provides pavement structural section recommendations based on the Orange County Highway Design Manual for the streets within County's jurisdiction. The Materials Lab performs field evaluations and pavement investigations consisting of drilling and coring the existing pavement for cost effective and environmental friendly rehabilitation recommendations.
Geotechnical Drilling and Sampling
The Materials Lab uses a truck mounted drill rig, CME-55 and a track mounted drill rig CME-850 with 8-inch diameter hollow stem augers for geotechnical drilling to determine the subsurface soil properties. Relatively undisturbed drive soils samples are obtained using California Split Spoon Sampler (2.5-inch inside diameter and 3.0-inch outside diameter) lined with 1-inch geotechnical sample rings. Standard Penetration Tests (SPT) are performed in the field using a standard split-barrel sampler (1.5-inch inside diameter and 2.0-inch outside diameter) driven in to the soil by a 140 pound automatic hammer falling through a 30-inch free fall. The sampler is driven 18 inches, and the number of blows are recorded for each 6-inch to characterize the subsurface soils.
Asphalt and Concrete Coring
Materials Lab uses a truck mounted drill rig, CME-45C and a portable coring machine with portable water supply for coring asphalt pavement and coring concrete retaining walls, concrete liner for flood control channels when there is insufficient compaction, when there are questionable defects in the asphalt concrete pavement or to verify the compressive strength of a concrete retaining wall or concrete channel liner.
Asphalt Concrete is inspected during production. Inspectors are well equipped with sieves, a balance, and other tools to run tests at the plant and make mix design modifications to assure specification compliance. Asphalt mix designs are approved by the Lab prior to shipping.
Portland Cement Concrete
Portland Cement Concrete is inspected during production. Inspectors check weighing of aggregates, cement, water, and admixtures to insure compliance with previously approved mix design. Inspectors also obtain samples of aggregate to be transported to the Materials Lab for testing. Concrete mix designs are approved by the Lab prior to shipping. Technicians will also perform "slump" tests and fabricate concrete cylinders for strength tests.
Rock Slope Protection
Inspectors are qualified to inspect Rip-Rap at the jobsite as well as at the source.
Inspectors are equipped with a set of sieves to perform sieve analysis of aggregate base on the grade or at the manufacturing plant. Samples are obtained and transported to the Materials Lab for further testing
Prefabricated Concrete Products
Reinforced Concrete Pipe Inspectors visually inspect RCP at the manufacturing plant for "Greenbook" compliance as well as witness D-Load testing of individual pipes. Prestressed Concrete Products Inspectors check forms, observe pre-stressing, inspect concrete and fabricate concrete cylinders to be transported to the Lab.
Cement Treated Base - The purpose of Cement Treated Base is to recycle crushed pavement and treat with cement and water to produce a firm and unyielding base material with a high gravel equivalent. Field inspection of Cement Treated Base is achieved with a crew of 1 or 2 technicians and 1 inspector. The crew performs compaction tests and "squeeze" tests for quality control of this process.
- Soil Cement - This material is used mainly for slope protection. The stabilization contractor assembles an onsite plant to manufacture soil cement. Inspection is similar to Cement Treated Base.
- Lime Treated Soil - This process treats clayey soil with calcium oxide to stabilize the soil and therefore increase the R-Value. Inspection of this material usually involves one inspector.
Physical and Chemical Testing
The Physical and Chemical Testing Section performs a multitude of quality control tests of concrete aggregates, asphalt concrete aggregates, rock slope protection, stabilized soil and native soil. Some of the major are: Sand Equivalent, Cleanness Value, Sieve Analysis, Hydrometer Analysis, Sulfate Content, Specific Gravity, Direct Shear, pH content and LART (Los Angeles Abrasion Test). This section also determines R-Value for structural sections and tests compressive strength of PCC cylinders, shotcrete cubes and soil cement.
The Compaction Testing Section performs in-place density tests at jobsites using Troxler nuclear density gauges. There are two subsections of this section: AC Compaction Testing and Soils/AB Compaction Testing.
The AC Compaction team performs in-place density tests with a Troxler thin-lift density gauge. Relative Compaction is calculated using the maximum density of a grade sample tested at the Materials Lab.
The Soils/AB Compaction team performs in-place density tests with a Troxler soils density gauge, obtains soil samples from the location of the test, and transports the soil samples to the Materials Lab to determine the maximum density.
The Asphalt Testing Section performs state-of-the-art physical and chemical testing of bituminous mixes.
Independent Assurance Testing
The Independent Assurance Testing (IAT) program allows Caltrans Independent Assurance (IA) personnel to test Materials Lab engineering technicians. If they qualify to perform Caltrans tests, Caltrans IA will provide Certificates of Testing Proficiency. This enables the Materials Lab’s Caltrans certified technicians to oversee the County’s consultants who perform Caltrans tests.