Applied Engineering & Research

Our team of experts is renowned for troubleshooting concrete-related issues. We work with our clients to innovate concrete scanning and testing methods and provide real-world solutions that are cost-effective and support the project stakeholders’ goals. The solutions we have been able to provide include:

• Enhancing the quality of concrete construction via the mitigation of cracking. Achieving this objective is especially important for building watertight reinforced concrete reservoirs to minimize loss of water. The biggest rectangular reinforced concrete reservoirs recently built in Los Angeles are two headworks Silver Lake structures with holding capacities of 55M yd3 (Phase 1) and 68M yd3 (Phase 2) of water. They were constructed in 2014-2020. Our team participated in the construction of both reservoirs. Los Angeles Metropolitan Department of Water and Power engaged Twining as a consultant for developing specifications and conceptual concrete and construction sequence design to minimize cracking.
• Mobile laboratories are equipped to test fresh and hardened rapid-strength concrete. The curing of specimens is performed in conditions matching the temperature of concrete in pavement or structure.
• Fast-track construction of bridge hinges using rapid-strength concrete
• Emergency repair of airfield pavement. Ultra-rapid hardening concrete with calcium-sulfoaluminate cement is often produced with volumetrically measuring and continuously mixing mobile units.
• Placement of the last truckload of rapid strength concrete during California-first 55-hrs weekend rehabilitation of a pavement segment on RTE-10 in Pomona. For this project, Twining received the ACPA National Award of Excellence.
• Reservoir floors consisted of several hundred individually placed mass concrete slabs. During the construction of the second phase, the sequence of placement was optimized to minimize restraint by adjacent elements during the early, most intense phase of concrete volume changes. Construction of the second-phase giant structure was preceded by the development of a new generation of concrete specifications that were focused on reducing cracking potential, minimizing crack repairs, and enhancing the water tightness of the reservoir. The total volume of concrete used for the construction of the second reservoir was 90,000 yd3.
• All concrete elements, such as floor and roof slabs, walls, and columns, were massive and treated as mass concrete. Cracking minimization started with incorporating in specifications the concept of low-volume-change concrete. For the construction of the second phase reservoir, prospective contractors were provided with practical solutions for formulating concrete with three minimums: (1) heat generation, (2) thermal expansion & contraction, and (3) shrinkage. Special batching, curing, and thermal control provisions were a part of the cracking minimization protocol implemented during construction.

Petrography Tools

Scanning Electron Microscopy

Scanning Electron Microscopy (SEM) allows our team to examine materials at higher magnifications and with superior resolution than optical microscopes. When equipped with energy-dispersive x-ray spectrometers (EDS), the electron microscope allows in situ determinations of the chemical composition of an area of interest. Our Concrete Insight experts possess extensive experience in the use of SEM/EDS methods to study microstructural aspects of cement hydration and strength development, fly ash quality and characteristics, and durability mechanisms that include sulfate attack, alkali-aggregate reactions, salt weathering and freeze-thaw damage as influenced by deicers.

Condition Surveys

Twining’s team of concrete research and development experts has a background in geological fieldwork, which hinges on the compass and offers a seamless translation to investigating concrete in the field. We have extensive experience looking at flooring failures, stucco failures, excessive cracking, and a host of durability mechanisms in the field. This capability enhances the development of sound sampling plans and contributes key observations that help link findings under the microscope to performance in the field.

Optical Microscopy

One of Concrete Insight’s core competencies is classical petrography, which is the branch of geology that deals with the systematic description of rocks and minerals. Optical microscopes, which manipulate photons to produce the images that inform our understanding of the performance of a material, serve as the foundation of our work. In our flagship office in Boulder, CO, we house a full complement of Nikon microscopes for stereomicroscopy, transmitted light microscopy, and air void analyses.

Electrical Resistivity

Our team uses bulk electrical resistivity for a variety of purposes relevant to assessing the quality and durability of cementitious materials. Bulk resistivity measurements are the foundation of the Formation Factor, which provides a robust method to evaluate the potential durability of a concrete mixture. The Formation Factor is a central pillar in determining transport properties of concrete mixtures and developing service life models of the time to reach chloride corrosion thresholds for embedded steel reinforcement. Finally, we use bulk resistivity with residual expansion testing and quantitative microcracking measurements to determine the potential for damage to occur in concrete affected by the alkali-aggregate reaction.

Fluorescence

Concrete Insight uses fluorescent microscopy to highlight key aspects of concrete in both reflected and transmitted light. We use epoxy with fluorescent dye to stabilize fragile and damaged samples, which allows us to observe and document cracks and microcracks on polished slabs with great resolution. We produce thin fluorescent sections to the highest standards that allow us to measure the w/cm of hardened cementitious materials.

U.S. Army Corps of Engineers (USACE) Certification

Our laboratory is USACE-certified. This validation indicates that our personnel, equipment, and internal quality control measures meet the standards set by the USACE for quality control and quality assurance. Our certifications include the following:

• Aggregate – C 295 – Opt – Petrographic Examination of Aggregates for Concrete
• Concrete – C 457 – Opt – Air-Void System by Microscopic Determination
• Concrete – C 856 – Opt – Petrographic Examination of Hardened Concrete

We offer a USACE-accredited laboratory for petrographic examination and analysis of aggregate materials and hardened concrete. Materials that commonly find their way to our shop include:

Petrographic & Materials Investigations

Our concrete research and development team uses concrete petrography and other analytical methods to investigate concrete and other cement-based construction materials, natural rock products, and geological resources. With straightforward thinking, meticulous detail, and impeccable customer service, we provide our clients with the information they need to understand the performance of construction materials.

Petrographic examination is useful for identifying aggregates that are susceptible to alkali-aggregate reactions, lack freeze-thaw durability, are soft or incompetent, have deleterious coatings or excessive fines, and more. DRP has extensive experience with aggregate QA/QC for use in concrete or other cement-based materials following procedures described in ASTM C295, Guide for Petrographic Examination of Aggregates for Concrete. We have done a petrographic examination on aggregates from all over North America, Central and South America, Asia, and scattered Pacific Islands.

Our team of experts is available to provide a wide range of solutions for your concrete projects, from providing quality assurance to diagnosing causes of deterioration. With extensive experience in concrete materials and early age problems, durability mechanisms, and the performance of slabs ranging from pavements to industrial floors, we help engineers formulate solutions that range from minor repairs to removal and replacement. We can provide: