Christopher C. Ferraro

Effect of Early Age Strength on Cracking in Mass Concrete Containing Different Supplementary Cementitious Materials: Experimental and Finite-Element Investigation

AbstractThis paper presents the findings of an investigation using the finite-element method to predict the distribution of temperatures within a hydrating massive concrete element. The temperature distribution produced by the finite-element thermal analysis of the model is used in the finite-element structural analysis to quantify the maximum allowable internal temperature difference before cracking will initiate in the concrete. To verify the results obtained in the finite-element model, four different mixes of concrete, typical for use in mass concrete applications in Florida, were produced and each mix was used to make two large-scale 1.07  m×1.07  m×1.07  m (3.5  ft×3.5  ft×3.5  ft) concrete blocks. The mechanical and thermal properties of early age concrete used values obtained experimentally from the concrete used to construct the four sets of blocks. The temperature distributions produced by the model were shown to be very similar to those measured in the experimental blocks. Results suggest that ...

Sulfate Attack on Concrete: Effect of Partial Immersion

Traditionally, the extent of sulfate attack is qualified through visual rating or quantified by the percent expansion of slender bars completely submerged in sulfate solution. There are currently no standardized test methods that take into account the change in engineering properties because of deleterious mechanisms. Moreover, the exposure regime used to evaluate sulfate attack, complete immersion, is not typically representative of that encountered in the field. For these reasons, the objective of the research presented herein is to quantify the degree of sodium sulfate attack through the degradation of mechanical properties, specifically the compressive and splitting tensile load capacities of standard cylindrical specimens. A novel exposure regime is utilized wherein the specimens are only partially submerged in 5% sodium sulfate solution, creating an evaporation front similar to that of field exposure. It was found that the portion submerged in sulfate solution, although visually pristine, was the weaker portion of the cylinder for both mechanical tests, even though the other half showed extensive signs of surface disintegration caused by salt crystallization.

Use of leaching tests to quantify trace element release from waste to energy bottom ash amended pavements

A series of roadway tests strips were paved on-site at a landfill in Florida, U.S. Waste to energy (WTE) bottom ash was used as a partial course aggregate replacement in a hot mix asphalt (HMA) and a Portland cement concrete (PCC) pavement, along with control HMA and PCC sections. This allowed for a comparison of the relative degree of leaching between both materials (HMA and PCC) as well as between the ash-amended and control pavements. Batch and monolithic tank leaching tests were conducted on the pavements. Testing of the PCC samples demonstrated that Mo and Al were elevated above regulatory thresholds for both the control and ash amended samples. Further leach testing demonstrated that the release of Mo was likely from the PCC and not a result of the inclusion of the BA into pavement. Batch leach testing of ash-amended HMA samples revealed Sb as a constituent of potential concern. The results of the monolith leaching test displayed leaching of Sb within the same order of magnitude as the regulatory threshold. Calculation of the leachability index (LI) for Sb found that it would have limited mobility when incorporated in the HMA matrix.

Detection and Assessment of Structural Flaws in Concrete Bridges with NDT Methods

Researchers investigated the applicability of various nondestructive testing (NDT) methods on full-scale concrete bridge structures, including ultrasonic pulse velocity tomography and the impact-echo method. The combination of the two methods enabled researchers to three-dimensionally evaluate material consistency and locate flaws or regions of deterioration within structural members with a new level of efficiency. Although research involving NDT methods has been conducted for many years, the use of NDT methods for primary investigation of full-scale structural elements is not typically performed. In this study, the investigation of bridge structures for flaws and damage resulted in the discovery of a previously undetected yet recurring form of damage, which led investigators to suspect a design flaw. The results of the ultrasonic pulse velocity tomography enabled researchers to assess the actual cause of the damage, which allowed the formulation of recommendations for the repair and redesign of the defective structural elements.

Construction material properties of slag from the high temperature arc gasification of municipal solid waste

Slag from the high temperature arc gasification (HTAG) of municipal solid waste (MSW) was tested to evaluate its material properties with respect to use as a construction aggregate. These data were compared to previously compiled values for waste to energy bottom ash, the most commonly produced and beneficially used thermal treatment residue. The slag was tested using gradations representative of a base course and a course aggregate. Los Angeles (LA) abrasion testing demonstrated that the HTAG slag had a high resistance to fracture with a measured LA loss of 24%. Soundness testing indicated a low potential for reactivity and good weathering resistance with a mean soundness loss of 3.14%. The modified Proctor compaction testing found the slag to possess a maximum dry density (24.04kN/m(3)) greater than conventionally used aggregates and WTE BA. The LBR tests demonstrated a substantial bearing capacity (>200). Mineralogical analysis of the HTAG suggested the potential for self cementing character which supports the elevated LBR results. Preliminary material characterization of the HTAG slag establishes potential for beneficial use; larger and longer term studies focusing on the materials possibility for swelling and performance at the field scale level are needed.

Rebar Detection with Cover Meter and Ultrasonic Pulse Echo Combined with Automated Scanning System

A sufficient concrete cover is essential to ensure the durability of reinforced concrete structures. Nondestructive testing methods that can measure the concrete cover are therefore promising tools. As a part of a research project funded by the Florida Department of Transportation, the capabilities and limitations of cover meter measurements in relation to this testing problem were investigated. Researchers designed a reinforced concrete test block on which properties such as rebar depth, size, and spacing and number of reinforcement layers were varied; the effects these variations had on the measurements were studied. The use of an automated testing frame consisting of two scanners that examined the test block from both sides ensured high positioning accuracy and constant quality in data acquisition and made possible the collection of the data along an extremely dense grid. In addition to the cover meter measurements, which referred only to the cover of the layer closest to the surface, ultrasonic pulse echo measurements were conducted, and a synthetic aperture focusing technique was applied to the data to make the rebars become apparent in refined B-scan images.

Ultrasonic linear array validation via concrete test blocks

Oak Ridge National Laboratory (ORNL) comparatively evaluated the ability of a number of NDE techniques to generate an image of the volume of 6.5′ X 5.0′ X 10″ concrete specimens fabricated at the Florida Department of Transportation (FDOT) NDE Validation Facility in Gainesville, Florida. These test blocks were fabricated to test the ability of various NDE methods to characterize various placements and sizes of rebar as well as simulated cracking and non-consolidation flaws. The first version of the ultrasonic linear array device, MIRA [version 1], was one of 7 different NDE equipment used to characterize the specimens. This paper deals with the ability of this equipment to determine subsurface characterizations such as reinforcing steel relative size, concrete thickness, irregularities, and inclusions using Kirchhoff-based migration techniques. The ability of individual synthetic aperture focusing technique (SAFT) B-scan cross sections resulting from self-contained scans are compared with various processing, analysis, and interpretation methods using the various features fabricated in the specimens for validation. The performance is detailed, especially with respect to the limitations and implications for evaluation of a thicker, more heavily reinforced concrete structures.

Tensile Strength Prediction in Concrete Using Nondestructive Testing Techniques

Field studies have suggested that wave velocities through concrete samples decrease with increasing damage. However, to date there has been no replication of this effect in a laboratory setting allowing for a controlled experiment to quantify this effect. The primary objective was to see how the exposure of concrete to sulfate solutions related to surface-wave velocity and through-wave velocity. The impact–echo method and the ultrasonic pulse velocity test were used to quantify these relationships, respectively. Laboratory research focused on correlating nondestructive test (NDT) data with destructive test results from field-sized concrete samples exposed to continuous sulfate attack over time. The intent was to evaluate the capabilities of the NDT techniques in identifying and quantifying damage due to sulfate attack. Prior research has shown that tension testing tends to be far more sensitive than compression testing to such damage. As a result, it was expected, and confirmed, that stress wave velocities from the two NDT techniques correlate better with tensile strength than with compressive strength.

Measuring Rock Strength While Drilling Shafts Socketed into Florida Limestone

AbstractThe focus of this research was the real time assessment of rock strength during drilled shaft installations in Florida. Measures of unconfined compressive strength, a function of rock stren...

Characterisation and management of concrete grinding residuals

Concrete grinding residue is the waste product resulting from the grinding, cutting, and resurfacing of concrete pavement. Potential beneficial applications for concrete grinding residue include use as a soil amendment and as a construction material, including as an additive to Portland cement concrete. Concrete grinding residue exhibits a high pH, and though not hazardous, it is sufficiently elevated that precautions need to be taken around aquatic ecosystems. Best management practices and state regulations focus on reducing the impact on such aquatic environment. Heavy metals are present in concrete grinding residue, but concentrations are of the same magnitude as typically recycled concrete residuals. The chemical composition of concrete grinding residue makes it a useful product for some soil amendment purposes at appropriate land application rates. The presence of unreacted concrete in concrete grinding residue was examined for potential use as partial replacement of cement in new concrete. Testing of Florida concrete grinding residue revealed no dramatic reactivity or improvement in mortar strength.