Search

Incorporation of fly ash in cementitious systems containing ordinary portland cement (OPC) increases their long-term strength and durability. However, replacement of cement by fly ash also reduces the heat of hydration of such systems and reduces early-age strength development. The reduced rate of strength development can increase the risk of durability problems, e.g. scaling, in cases when young concrete is exposed to low temperatures and deicing chemicals. This study investigated the potential of nano-titanium dioxide (nano-TiO2) particles to modify the hydration kinetics of fly ash pastes and compressive strength development of corresponding mortars cured under low (4°C) and standard (23°C) temperatures. The kinetics of the hydration study was performed on paste specimens using the thermogravimetric analysis (TGA) and isothermal calorimetry (IC) methods. The mortar specimens used for compressive strength testing were prepared using the same w/cm values and the same types of binders as those used to prepare the paste specimens. It was found that although the addition of nano-TiO2 accelerated the hydration rate of all pastes, that treatment was, however, more effective in the fly ash pastes than in the ordinary portland cement (OPC) pastes, especially for the cases of low temperature curing. These findings were confirmed by the results of strength testing as the specimens experiencing accelerated rates of hydration were also found to be stronger.

As the most widely used construction material, concrete is very durable and can provide long service life without extensive maintenance. The strength and durability of concrete are primarily influenced by the initial water-cement ratio value (w/c), and the curing condition during the hardening process also influences its performance. The w/c value is defined as the total mass of free water that can be consumed by hydration divided by the total mass of cement and any additional pozzolanic material such as fly ash, slag, silica fume. Once placed, field concrete pavements are routinely cured with liquid membrane-forming compounds. For laboratory study, concrete samples are usually cured in saturated lime water or a curing room with a relative humidity (RH) value higher than 95%. Thus, the effectiveness of curing compounds for field concrete needs to be studied. In this study, the dielectric constant value of plastic concrete was measured by ground penetrating radar (GPR). The w/c value of the plastic concrete was calculated by a mathematical model from the measured dielectric constant value. The calculated w/c value was compared with the microwave oven drying measurement determined result in AASHTO T318. A modified coarse aggregate correction factor was proposed and applied in microwave oven drying measurement to determine the w/c value of plastic concrete in AASHTO T318. The effectiveness of curing compound was evaluated by field concrete slabs by GPR measurement. It was found that GPR can be a promising NDT method for In this study, the dielectric constant value of plastic concrete was measured by ground penetrating radar (GPR). The w/c value of the plastic concrete was calculated by a mathematical model from the measured dielectric constant value. The calculated w/c value was compared with the microwave oven drying measurement determined result in AASHTO T318. A modified coarse aggregate correction factor was proposed and applied in microwave oven drying measurement to determine the w/c value of plastic concrete in AASHTO T318. The effectiveness of curing compound was evaluated by field concrete slabs by GPR measurement. It was found that GPR can be a promising NDT method for w/c determination of plastic concrete and curing effectiveness evaluation method for hardened concrete.

In a book published in 1906, Richard Meade outlined the history of portland cement up to that point1. Since then there has been great progress in portland cement-based construction materials technologies brought about by advances in the materials science of composites and the development of chemical additives (admixtures) for applications. The resulting functionalities, together with its economy and the sheer abundance of its raw materials, have elevated ordinary portland cement (OPC) concrete to the status of most used synthetic material on Earth. While the 20th century was characterized by the emergence of computer technology, computational science and engineering, and instrumental analysis, the fundamental composition of portland cement has remained surprisingly constant. And, although our understanding of ordinary portland cement (OPC) chemistry has grown tremendously, the intermediate steps in hydration and the nature of calcium silicate hydrate (C-S-H)*, the major product of OPC hydration, remain clouded in uncertainty. Nonetheless, the century also witnessed great advances in the materials technology of cement despite the uncertain understanding of its most fundamental components. Unfortunately, OPC also has a tremendous consumption-based environmental impact, and concrete made from OPC has a poor strength-to-weight ratio. If these challenges are not addressed, the dominance of OPC could wane over the next 100 years. With this in mind, this paper envisions what the 21st century holds in store for OPC in terms of the driving forces that will shape our continued use of this material. Will a new material replace OPC, and concrete as we know it today, as the preeminent infrastructure construction material?

This paper summarizes the results of sulfate resistance study of carbonated mortar specimens made with Solidia CementÔ (SC) and tested for expansion according to ASTM C1012 specification while exposed to three types of soak solutions: sodium sulfate, magnesium sulfate and deionized water. A control set of ordinary portland cement (OPC) mortars was also evaluated. Besides the length change measurements, visual observations of changes in the appearance of specimens were conducted after various lengths of exposure. In addition, microstructural characterization of the specimens was conducted using scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermo-gravimetric analysis (TGA) techniques. Finally, changes in the concentration of the chemical species present in the soak solutions in contact with the SC specimens were evaluated using both, the ion chromatography (IC) and the inductively coupled plasma optical emission spectrometry (ICP-OES). As expected, the OPC mortar specimens started deteriorating early and reached the critical (i.e.0.1%) level of expansion in about 4 months in case of sodium sulfate solution and in about 6 months in case of magnesium sulfate solution. With respect to the SC mortar specimens, those exposed to magnesium sulfate solution showed higher expansion than those exposed to sodium sulfate solution. However, after 18 months of exposure to both types of sulfate solutions the maximum expansion levels of specimens were still only about 33% of the critical (value. The SEM examination of SC mortar bars indicated that the matrix of the specimens exposed to magnesium sulfate solution showed evidence of formation of gypsum and magnesium-silica compounds. Magnesium and sulfate ions seem to have altered the morphology of the carbonation-generated silica phase and produced gypsum deposits in the air-voids, within the matrix and at the paste – aggregate interfaces. The formation of gypsum in those specimens was confirmed by the results of thermal and XRD analyses. Finally, the ionic analysis of the magnesium sulfate soak solution indicated consumption of sulfate ions whereas the concentration of the sulfates in sodium sulfate soak solution didn’t change during the exposure period.

High early strength (HES) concrete is becoming increasingly used to repair damaged concrete pavement sections. The use of HES concrete enables the repaired pavement to be opened to traffic within hours of placing the concrete. Rapid repair of concrete pavement is an attractive solution since the traveling public is not delayed by the repair of the pavement in addition to a decrease in the amount of exposure to traffic by construction personnel; however, there are challenges due to strict requirements for opening strength and severe penalties for not achieving the target strength. This project examined failure to obtain long term strength in the construction practices of long patches in concrete pavements. The work examined issues associated with temperature on sulfate balance, flexural strength prediction (maturity methods) considering the influence of moisture (effects of self-desiccation), shrinkage mitigation techniques (internal curing), and improving the overall durability of HES concrete patching materials.

There is an increasing interest in hierarchical design and Additive Manufacturing (AM)of cement-based materials. However, the brittle behavior of these materials and the presence of interfaces from the additive manufacturing process represent the current major challenges. Our work focuses on harnessing the heterogeneous interfaces by employing clever designs from bio-inspired Bouligand architectured materials. In this paper, we aim to demonstrate some key mechanisms that can allow brittle hardened cement-based materials to gain flaw-tolerant properties. Mechanisms such as cracktwisting at the interfaces have been previously observed in naturally-occurring orsynthetic composite Bouligand architectures. In this paper, a heterogeneous interface with porous characteristics in 3D-printed solid hardened cement paste (hcp)architectures were characterized. We hypothesize that the presence of heterogeneous interface in 3D-printed hardened cement paste (hcp) elements, in conjunction with clever architectures, promote key damage mechanisms such as interfacial cracking and crack twisting that lead to damage delocalization. This delocalization can be energetically favorable and allow energy dissipation and promote toughening and flaw-tolerant properties. We found that these architectures can enhance the properties from the typical strength-porosity relationship, classically known for brittle hcp materials.

There is an increasing interest in the fabrication of cement-based materials via additive manufacturing (AM) techniques. However, the processing-induced heterogeneities and interfaces represent a major challenge. The role of processing in creating interfaces and their characteristics requires understanding of the microstructure of 3D-printed hardened cement paste (hcp). This work investigates the microstructural features of architectured cement-based materials, including processing-induced heterogeneous patterns, interfacial regions (IRs), and pore network distributions with respect to the architectural pattern. A 3D printer was modified and merged with an extrusion system and specimens were 3D-printed using a layer-wise direct ink writing (DIW) process capable of fabrication of lamellar architectures of materials. A lab-based X-ray microscope (XRM) was used to perform X-ray micro-computed tomography (micro-CT) evaluations to explore the microstructural characteristics of 3-day old intact (i.e. not tested) 3D printed and cast specimens at two levels of magnification: 0.4X and 4X. CT scans of printed specimen revealed a patterned pore network and several microstructural features, including: a) macropores, b) micropores at interfacial regions (IRs), c) accumulation of anhydrous cement particles near macropores, and d) rearrangement of filaments away from their designed toolpath. In comparison, microstructural investigation of cast specimen at 4X scan revealed randomly distributed pores with no connectivity throughout the specimen. The aptitude of micro-CT as a non-destructive technique for microstructural characterization is discussed. The role of processing to induce and to pattern heterogeneities such as IRs in materials is demonstrated and the role of architecture in controlling such heterogeneities and their directionality through the interface is discussed.

Concrete pavements represent a large portion of the transportation infrastructure. While the vast majority of concrete pavements provide excellent long-term performance, a portion of these pavements have recently shown premature joint deterioration. Substantial interest has developed in understanding why premature joint deterioration is being observed in jointed portland cement concrete pavements (PCCP). While some have attributed this damage to insufficient air void systems, poor mixture design, or chemical reaction between the salt and the paste, it is the hypothesis of this work that a component of this damage can be attributed to fluid absorption at the joints. This report begins by discussing the importance of the level of concrete saturation on freeze-thaw damage. Second, this report describes the influence of deicing salt solutions on drying and wetting of concrete. Third, the report describes some observations from field studies. Fourth, the report discusses soy methyl esters polystyrene blends (SME-PS) as a potential method to extend the service life of concrete pavements by limiting the ingress of salt solutions. The report also discusses field application of the SME-PS blends for field investigation. Finally, the report discusses the development of a test to assess chloride solution ingress during temperature cycling. The aim of this work is to provide background on some aspects that can lead to joint deterioration and to provide the pavement community alternatives on how sealers and deicers may be able to be used more efficiently to reduce joint damage.

The objective of this research was to develop and test high performance concrete mixtures, made of locally available materials, having durability characteristics that far exceed those of conventional concrete mixtures. Based on the results from the development of high performance concrete, guidelines for a high performance concrete bridge over Burnett Creek on SR 43, just north of I-65 near West Lafayette, Indiana, will be prepared. In addition, the effects of different curing conditions, with respect to temperature and moisture conditions, were evaluated. The use of 15.2 mm (0.6 in) prestressing strand in girders made of 69 MPa (10 ksi) concrete was also evaluated with respect to pullout resistance and transfer and development lengths.

This study was initiated to continue monitoring of the performance of five test sections placed in 1997 to compare the performance of Superpave asphalt mixtures with different binder grades and one test section designed using the Marshall mix design method. A previous study had evaluated the performance of these test sections for four years after construction. This study extended that evaluation period to 12 years. During that time period, cores were taken from each test section at 9.5 and 12 years in service. Cores were tested and analyzed to determine the volumetrics and low temperature cracking behavior of the mixtures. Additional cores were used to extract, recover and test the binder in the mixtures. Results showed that the air void content in the mixtures did continue to decrease up to about nine years then appears to have leveled off. Aging (stiffening) of the unmodified binders was observed through Dynamic Shear Rheometer testing of the recovered binders but not by the penetration test. The modified binder did not exhibit the same level of aging as the unmodified binders. Aging also affected the recovered low temperature binder grade of four of the six binders, but the other two seemed relatively insensitive to aging at low temperatures. Testing of field cores showed that all of the mixtures would be expected to show thermal cracking at 9.5 years and beyond; this was confirmed by field distress surveys. The mix with polymer modified binder showed the greatest amount of cracking, which began at an early age in the field; this was not expected and did not correlate well with the lab testing results for unknown reasons. The mix with 15% RAP was slightly stiffer than a companion control mix without RAP, but the difference in predicted cracking temperature was only 1 - 2°C for the surface mixes. Based on these results, INDOT can continue to use Superpave mixes with confidence, especially when considering the fact that Superpave has continued to evolve and be refined since this project was constructed. The mixture with RAP has performed about as well as the virgin mixtures under heavy interstate traffic.

The fresh concrete water-cement ratio (w/c) determination tool is urgently needed for use in the QC/QA process at the job site. Various techniques have been used in the past to determine this parameter. However, many of these techniques can be complicated and time consuming. Furthermore, extensive calibration is often needed to correlate the properties measured by these techniques with w/c. During the course of the present study, the method for the use of the unit weight for the determination of w/c of fresh concrete has been developed and evaluated on both laboratory and field concretes. Additionally, the accuracy of using microwave oven technique for w/c determination reported by previous research was confirmed. Finally, the accuracies of unit weight and microwave oven techniques for the determination of w/c were compared. The unit weights required for this method have been determined either by using a “zero-air” procedure (ZAP) developed as a part of this study or by using conventional (following AASHTO specifications) methods. The ZAP technique was used to verify the w/c of 58 different laboratory concrete mixes. These verification efforts revealed that the minimum, maximum, standard error, and 95th percentile of the differences (∆w/c) between batched and determined w/c were, respectively, 0.000, 0.042, 0.017, and 0.030. The AASHTO determined unit weight (which also required measurements of the actual air content of concrete) was used to verify the w/c values of an additional set of 57 laboratory mixes. When using the AASHTO unit weights (and air contents) the minimum, maximum, standard error, and 95th percentile of ∆w/c were, respectively, 0.000, 0.075, 0.030, and 0.054. In addition, the AASHTO unit weight method was also used to verify the w/c values of 22 different field mixtures. For this case, the differences (∆w/c) between the design and unit weight-calculated values of w/c were in the range ±0.030 for all but one mixture. Finally, direct comparison of the results from the proposed method with the results obtained from the microwave oven method revealed that the former is faster but slightly less accurate. Specifically, when used on five separate concrete samples, the accuracy of the microwave oven method was 0.010, much smaller than the previously mentioned values of 0.030 (for the ZAP) and 0.054 (for the AASHTO) unit weight methods.

In 2003, the Indiana Department of Transportation and the Federal Highway Administration allowed a test section of Porous Friction Course (PFC) to be placed on I74 east of Indianapolis. The design, construction and early performance of that surface were compared to an adjacent SMA surface and a conventional Superpave HMA surface in a report prepared for the Institute for Safe, Quiet and Durable Highways (1). The early performance indicated that the PFC offered several advantages over the SMA and the conventional surfaces, including reduced tire/pavement noise, high friction and surface texture, and reduced splash and spray. There was a concern, however, that porous surfaces can lose their porosity, and therefore their performance advantages, over time. Consequently, the project summarized in this report was planned to continue monitoring the performance of the PFC and the comparison surfaces in order to investigate the durability of the porous surface over a five-year period (after construction). After five years under traffic, there have indeed been some changes in these properties. Most of the changes, however, took place quickly as the asphalt binder film coating the exposed aggregate particles was worn off by traffic. Since then, the changes have been relatively minor. The PFC section is still significantly quieter than the adjacent SMA section to which it has been compared. The PFC has retained most of its texture and is still providing good friction levels. Both the PFC and the SMA are still in very good condition with little distress and have higher friction levels than a section of dense graded asphalt constructed with similar materials that has also been evaluated for the duration of the study.

Joints are placed in Portland cement concrete pavements (PCCP) to control random cracking. These joints provide a weakened plane that enables a crack to form in a controlled manner, relieving residual stresses that develop when thermal, hygral, or hydration movements are resisted by sub grade and adjoining pavement. While the concept of creating a weakened plane through saw-cutting is straightforward, determining the time and depth of the saw-cut has proven to be complicated. The goal of this project was to reduce the risk for joint raveling and random cracking. Specifically, this project has focused on: developing a procedure for determining the appropriate saw-cutting time window for typical pavements constructed in the state of Indiana, determining the depth of the saw-cut that minimizes the risk of micro-cracking and random crack development, and developing tools and training materials for paving contractors and state inspectors that aid in implementing the findings of this study in concrete pavements. Toward this end the project was divided into three phases. The first phase of the project consisted of shadowing five pavement projects in Indiana. From these field investigations practical information was gained which was useful in developing the laboratory testing program. The second phase of this work involved in the development of the laboratory testing program. This phase in large part was involved in the development and commissioning of a new tensile wedge testing approach to determine the early age properties of concrete. Finally, finite element simulations were performed to simulate the early-age behavior of pavements constructed under a variety of saw-cutting sequences, environmental conditions. A strength reduction factor was computed based on the depth of the saw-cut. It was shown that the time of the saw-cut introduction needs to occur before the residual stress divided by the product of the strength reduction factor and tensile strength was equal to unity. It was also shown that shallower saw-cut depths were more prone to construction and material property variability. Recommendations are made to assist contractors in determining when saw-cuts are placed that can greatly improve field operations.

Ultra-Thin Whitetopping (UTW) is a pavement rehabilitation technique that involves the placement of a thin Portland Cement Concrete (PCC) overlay, 2 inches (50 mm) to 4 inches (100 mm) thick, over a distressed Hot Mix Asphalt (HMA) pavement. Typically, the HMA pavement is milled and cleaned which helps to create a bond between the existing HMA pavement and the PCC overlay. The bond between the two layers promotes composite action of the pavement section and as a result has a direct impact on the performance of the UTW Pavement. This composite action allows for the reduced thickness in the UTW layer. Additionally, a short joint spacing is typically used, which reduces the UTW flexural and curling stresses. In this study three different test areas were constructed in the INDOT/Purdue University Accelerated Pavement Testing facility. Each test area had different lanes that varied by concrete mix design, bonding preparation, and pavement crosssection. These sections were subjected to 300,000 to 560,000 load applications. An additional test area was constructed outside the facility to evaluate pavement thicknesses and environmental effects. The project resulted in a modified UTW design methodology that takes into account the stiffness of all underlying pavement layers. Additionally, the project provides insight into the effects of pavement section, UTW mix design, mechanical loading, bond conditions, and environmental loading on the performance of UTW.