Paul Fuchs

Ultrasonic testing of reactive powder concrete

Concrete is a critical material for the construction of infrastructure facilities throughout the world. Traditional concretes consist of cement paste and aggregates ranging in size from 6 to 25 mm that form a heterogeneous material with substantial compressive strength and a very low tensile strength. Steel reinforcement is used to provide tensile strength for reinforced concrete structures and as a composite the material is useful for structural applications. A new material known as reactive powder concrete (RPC) is becoming available. It differs significantly from traditional concrete; RPC has no large aggregates, and contains small steel fibers that provide additional strength and, in some cases, can replace traditional steel reinforcement. Due to its high density and lack of aggregates, ultrasonic inspections at frequencies 10 to 20 times that of traditional concrete inspections are possible. This paper reports on the initial findings of research conducted to determine the applicability of ultrasonic testing techniques for the condition assessment of RPC. Pulse velocities for shear and longitudinal waves and ultrasonic measurement of the modulus of elasticity for RPC are reported. Ultrasonic crack detection for RPC also is investigated.

Thermoviscoelastic Analysis and Creep Testing of Ambient Temperature Cure Epoxies Used in Adhesive Anchor Applications

Thermoviscoelastic properties and creep response of two commercial ambient temperature cure epoxy structural adhesives were analyzed and compared. The adhesives were formulated by the same manufacturer and appeared to be chemically similar; however, one system contained accelerators to shorten its cure time. In the laboratory, dynamic mechanical temperature/frequency sweeps were performed on both systems to generate dynamic mechanical and creep compliance master curves using time-temperature superposition principles. Differences were observed in the dynamic mechanical properties of the two adhesive systems as well as in their calculated creep compliance, which have been attributed to differences in their curing agent(s) and accelerator(s). Full-scale creep tests were carried out on anchors installed in concrete slabs and subjected to sustained loads for 82 days. These results were in good agreement with the creep compliance estimated using time-temperature superposition, suggesting that dynamic mechanical...

Ultrasonic Testing for Quality Control of Ultra-high Performance Concrete

Ultra-high performance concrete (UHPC) is proposed as an innovative new material for the construction of highway bridge superstructures. UHPC mix designs typically include no aggregates larger than sand, and include steel fibers 0.2 mm in diameter and 13 mm in length. These steel fibers and special mix design increase the strength and toughness of the UHPC significantly relative to more traditional concretes. However, low water to cement ratios typically used result in difficult casting and curing conditions and as a result there is a need to evaluate strength and stiffness parameter of as-cast members. This research reports on the development of ultrasonic methods for monitoring the elastic properties of UHPC under a series of curing scenarios. Ultrasonic velocity measurements are used to estimate the bulk elastic modulus, shear modulus and Poisson’s ratio of UHPC and results are compared with traditional, destructive methods. Changes in ultrasonic velocities during curing and relationships to early-age strength of the materials are discussed. The application of ultrasonic testing for the evaluation of early-age material properties and for nondestructive, in-situ materials characterization are explored. The potential for the development of practical quality control techniques for the future implementation of UHPC is also discussed.

Ultrasonic measurement of the elastic properties of ultra-high performance concrete (UHPC)

This paper discusses research to develop ultrasonic methods for materials characterization of an innovative new material known as Reactive Powder Concrete (RPC). Also known as Ultra-high performance concrete (UHPC), this relatively new material has been proposed for the construction of civil structures. UHPC mix designs typically include no aggregates larger than sand, and include steel fibers 0.2 mm in diameter and 12 mm in length. These steel fibers increase the strength and toughness of the UHPC significantly relative to more traditional concretes. Compressive strengths of 200 to 800 MPa have been achieved with UHPC, compared with maximum compressive strength of 50 to 100 MPa for more traditional concrete materials. Young’s modulus of 50 to 60 GPa are common for UHPC. However, the curing methods employed have a significant influence on the strength and modulus of UHPC. This paper reports on the development of ultrasonic methods for monitoring the elastic properties of UHPC under a series of curing scenarios. Ultrasonic velocity measurements are used to estimate the bulk elastic modulus of UHPC and results are compared with traditional, destructive methods. Measurements of shear moduli and Poissons ratio based on ultrasonic velocity are also reported. The potential for the development of quality control techniques for the future implementation of UHPC is discussed.

Nondestructive Evaluation of Reactive Powder Concrete

Reactive powder concrete (RPC) has been introduced as a structural material for civil engineering applications. The material consists of a finely graded combination of cement, sand, ground quartz and silica fume which combined with water form a cement paste. Small steel fibers measuring approximately 0.2 mm in diameter and 12 mm in length are distributed throughout the cement matrix and the combined material has very high compressive strength and toughness. The material is proposed for use in the primary load bearing members in bridges, and as such nondestructive evaluation technologies are needed to evaluate material quality and monitor in‐service condition. This paper reports on research to determine the effectiveness of ultrasonic testing for determining the elastic properties of RPC. Comparison between static modulus of elasticity and ultrasonic modulus measurements is presented. A system for determining elastic moduli as a quality control tool is discussed. The effect of curing conditions on ultrason...

Instrumentation for load rating of bridges

A large percentage of the nations bridges are classified as structurally deficient or functionally obsolete. Many bridges are classified as such due to the bridges load rating. However, the vast majority of bridges are not actually tested to determine their load capacity. In general, actually testing a structure to determine the load rating is time consuming and expensive. As a result only a low number of bridges can be tested. A main time consuming portion of the load test is the setup of conventional instrumentation to monitor the status of the bridge under test. Typically strain gages and LVDT (or similar) deflection transducers are used. Instrumentation which would allow rapid load testing of bridges is currently being developed and tested at the Federal Highway Administration. This instrumentation includes wireless data acquisition systems interfaced with clamp-on strain gages, which can be placed at a measurement location in a matter of minutes. Also, the instrumentation includes a remote laser- based deflection measurement system. The combination of the two types of instrumentation, wireless data acquisition and laser-based deflection measurements, has the potential to allow a greater number of structures to be load rated giving a more accurate picture of the health of the nations bridges.