Daniel C. Jansen

Permeability study of cracked concrete

Cracks in concrete generally interconnect flow paths and increase concrete permeability. The increase in concrete permeability due to the progression of cracks allows more water or aggressive chemical ions to penetrate into the concrete, facilitating deterioration. The present work studies the relationship between crack characteristics and concrete permeability. In this study, feedback controlled splitting tests are introduced to generate crack width-controlled concrete specimens. Sequential crack patterns with different crack widths are viewed under a microscope. The permeability of cracked concrete is evaluated by water permeability tests. The preliminary results indicate that crack openings generally accelerate water flow rate in concrete. When a specimen is loaded to have a crack opening displacement smaller than 50 microns prior to unloading, the crack opening has little effect on concrete permeability. When the crack opening displacement increases from 50 microns to about 200 microns, concrete permeability increases rapidly. After the crack opening displacement reaches 200 microns, the rate of water permeability increases steadily. The present research may provide insight into developing design criteria for a durable concrete and in predicting service life of a concrete structure.

Testing of Concrete Under Closed-Loop Control

Abstract Closed-loop testing systems provide the ability to directly control the deformation of the loaded specimen. This considerably enhances the precision, stability, and scope of the experiments. Closed-loop machines can be used to determine the stable response of test specimen or structure by monitoring and controlling the physical quantities that are sensitive to its behavior. The importance of the various components of the closed-loop controlled system and the test configuration is reviewed in the paper. The most critical aspect of designing the test is the choice of the controlled variable. With appropriate controlled variables and good system performance, several interesting and intricate testing techniques can be developed, as seen in the examples presented here.

Postpeak Strain-Stress Relationship for Concrete in Compression

This paper aims to present a postpeak strain-stress relationship based on strain localization of concrete in compression. This relationship predicts differences in postpeak ductility of specimens with varying height-width ratios. Experimental stress-strain curves from compression tests of mortar, normal- and high-strength concrete, and fiber-reinforced concrete available in the literature were used to determine the empirical constants separately for each material. Once the constants are known, the postpeak compressive behavior for any specimen with a known practical height-width ratio greater than or equal to 2 can be calculated. Results indicate that the relationship accurately predicts an increase in postpeak ductility with a decrease in specimen height-width ratio for the mortar and concretes examined in this research.

Lightweight Fly Ash-Plastic Aggregates in Concrete

The potential of using a synthetic lightweight aggregate (SLA) in concrete is examined. The aggregates are manufactured through thermal processing using plastic to encapsulate and bind fly ash particles. Nominal maximum-size aggregates of 9.5 mm were produced with fly ash contents of 0 percent, 35 percent, and 80 percent by total mass of the aggregate. The plastic used was high-density polyethylene, and the fly ash had a carbon content of 12 percent. An expanded clay lightweight aggregate and a normal-weight aggregate were used as comparison. Gradation, specific gravity, and absorption capacity are reported for the aggregates. Five batches of concrete were made with the different coarse aggregate types. Volume fractions of cement, water, fine aggregates, and coarse aggregates were kept the same for comparative purposes. Mechanical properties of the concrete determined included density, compressive strength, elastic modulus, splitting tensile strength, fracture toughness, and fracture energy. Salt-scaling resistance, a concrete durability property, was also examined. Compressive and tensile strengths were lower for the synthetic aggregates than for the normal-weight and expanded clay lightweight aggregates; however, comparable fracture properties were obtained. Relatively low compressive modulus of elasticity was found for concretes with the SLAs, although high ductility was also obtained. As fly ash content of the SLAs increased, all properties of the concrete were improved. Excellent salt-scaling resistance was obtained with the SLA containing 80 percent fly ash.

Engineering Controlled Low Strength Materials Using Scrap Tire Rubber

An investigation was conducted to determine the influence of recycled scrap tire rubber on the engineering properties of controlled low strength material (CLSM). With control over the ultimate compressive strength of CLSMs being key for applications such as backfilling utility trenches where re-excavation is often necessary, incorporation of scrap tire rubber into the CLSM mixture is a viable way to limit the ultimate strength. The work presented includes the results of 27 batches of CLSM, 20 of which included scrap tire rubber. The variables included: cement content, fly ash content, and fractional replacement of sand with scrap tire rubber. Results show that incorporation of scrap tire rubber into CLSM mixtures can be an effective way to limit term strength gain although it adds its own complexity.

Physical Properties of Concrete with Vitrified Coarse Aggregate

This study examines the potential of using vitrified aggregate in concrete by comparing concrete made with natural coarse aggregate to concrete made with vitrified aggregate. For comparison purposes, volume fractions of cement, water, fine aggregates, and coarse aggregates are identical for both batches of concrete. Mechanical properties determined include compressive strength, tensile strength, fracture toughness, modulus of elasticity, Poisson ratio, density, and axial and lateral strains at peak stress. Salt scaling resistance, a durability property, is also examined. An environmental scanning electron microscope is used to explore the bond between the natural aggregate and mortar and the vitrified aggregate and mortar. Results show that at the microstructural level, the surface of the vitrified coarse aggregate is smooth in comparison with the surface of the natural coarse aggregate and that the physical bond between the vitrified coarse aggregate and mortar is poor. The poor bond resulted in a decrease in compressive and tensile strengths and fracture energy and correlated to a decrease in salt scaling resistance. An insignificant change in fracture toughness was found. A relatively large compressive modulus of elasticity was found for concrete with vitrified aggregates attributable to the stiffness of the vitrified aggregate; however, the elastic modulus from bending of fracture beams showed significantly less increase in elastic modulus.

Effectiveness of Water Jetting for Removal of Anomalous Materials from Drilled Shafts

Initial results from a parametric laboratory investigation are described: the investigation was designed to study the effectiveness of water jetting as a means for removal of anomalous materials from concrete drilled shaft foundations. A primary objective for the investigation was to establish relationships between jetting parameters and the removal of commonly occurring anomalous zone materials, including low-strength concrete, slurry-mixed concrete, grout, and clay soil. The experimental work consisted of water blasting test specimens with rotary jets, nozzles, and pumping equipment typically used in construction practice. During testing, material removal rates were measured as a function of jet pressure and standoff distance for specimens with compressive strengths ranging between approximately 5 and 6,500 psi. Water-blasted specimens were cut apart after testing to confirm erosion measurements and to permit inspection of the water-blasted surfaces. The results show that erosion rates and the effectiveness of water jetting are primarily influenced by compressive strength when standard test equipment and jetting pressures are used. The size and angularity of aggregate in the anomalous material do not appear to influence erosion. The greatest erosion was observed for a semicemented material with a compressive strength of approximately 500 psi. Maximum erosion was observed approximately 12 in. from the axis of the jet.

Analysis and Seismic Performance Evaluation of Flexure-Dominated Interlocking Compressed Earth Block Walls:

This paper presents development and validation of three analytical models for flexure-dominated Interlocking Compressed Earth Block (ICEB) walls, which are based on classic mechanics of materials, inelastic truss elements, and phenomenological hysteretic model, respectively. Based on the testing results from a prior experimental investigation, it is shown that the first two models provide reasonable estimates for the lateral load resistance of flexure-dominated ICEB walls and the third model captures the inelastic behavior of flexure-dominated ICEB walls under cyclic loading. Using the third model, incremental dynamic analyses were conducted and performances of two demonstration single-story buildings consisting of flexure-dominated ICEB walls were evaluated for three construction sites with different levels of seismicity. Computer simulation results show that both demonstration buildings are able to avoid earthquake-induced collapse. It is also found that the current design and construction of flexure-dominated ICEB walls may be overly conservative for a site with relatively low seismicity.

Water Jetting to Mitigate Defects in Drilled Shafts: Laboratory Investigation

A laboratory investigation was designed to examine the effectiveness of water jetting as a means of removing anomalous (deleterious) material from drilled shafts. One objective of the investigation was to establish relationships between jetting parameters and the removal of common anomalous materials, including low-strength concrete, slurry-mixed concrete, grout, and clay soil. The experimental work consisted of blasting test specimens of anomalous material with water by using rotary jets, nozzles, pumping equipment, and testing procedures in current construction practice. During testing, erosion levels and rates were measured as a function of jetting pressure and standoff distance for specimens with compressive strengths ranging between approximately 5 and 6,500 pounds per square inch (psi). Erosion levels, erosion rates, and water-jetting effectiveness were found to correlate with the compressive strength of the anomalous material. Reinforcing steel bars in a drilled shaft influenced erosion levels and water-jetting effectiveness locally by interfering with the jet path. For jetting pressures around 10,000 to 11,000 psi, erosion was observed to a radial distance of approximately 12 in. from the axis of the water jet for the weakest specimen. The erosion distances observed during the investigation were less than half of the maximum design spacing typically used for drilled shaft access tubes installed for nondestructive testing.

Overview of High-Molecular-Weight Methacrylate for Sealing Cracks in Concrete Bridge Decks

Cracking in concrete bridge decks is widely regarded as a long-term durability and maintenance problem that requires attention. These cracks propagate through the deck and allow rapid ingress of moisture and chlorides into the concrete interior, leading to excessive deterioration from rebar corrosion. In California, high-molecular-weight methacrylate (HMWM) is frequently used as a crack sealer, with millions of dollars spent annually on maintenance applications of methacrylate on state-owned bridges. The work presented reviews previous research regarding the effectiveness of concrete bridge deck sealers and the results of a nationwide survey investigating the effectiveness and state of practice of using methacrylate as a crack and surface sealer. Although a wide range of application temperatures was reported in the literature, application temperatures between 7°C and 29°C are generally recommended. Cracks should be sealed as soon as possible to ensure that chloride concentrations do not reach the corrosion threshold value. For old decks, careful attention should be paid to the preparation method and cleanliness of both the deck surface and cracks. For areas not subjected to deicing chemicals and chloride-laden environments, HMWM can nearly restore the full bond and flexural strength if the cracks are narrow and free of contaminants.