Wash water is generated as a by-product of ready mixed concrete production. Reuse of the water as mixture water is limited, in practice, by the negative material performance impacts associated with the water chemistry and suspended solids (i.e. hydrating binder phases and very fine aggregate); the effects are intensified with increasing content of suspended solids and water age. A novel carbon dioxide treatment to allow the use of high solids wash water as mixture water was examined through mortar and concrete testing. An industrially sourced wash water with a specific gravity of over 1.20 was treated with CO 2 . Seven batches of concrete were produced and compared: a reference mixture at three different w/b, and four batches with a 6% reduction in cement where wash water was used as mixture water (diluted to a specific gravity of 1.08, comparing untreated versus CO 2 treated conditions, aged either 1 day or 5 days). The treatment mineralized CO 2 at 27% by weight of the cement in the solids and reduced or eliminated negative aspects associated with the untreated water (set acceleration, workability loss, strength reduction with water age). The CO 2 -treated solids displayed latent hydraulicity. The approach allows three waste streams (CO 2 , wash water and wash water solids) to be reused to produce more sustainable concrete.

The research described herein was conducted as a part of NCHRP Project 18-04B, Early Opening-to-Traffic Portland Cement Concrete for Pavement Rehabilitation [Van Dam TJ. Durability of ‘Early-Opening-to-Traffic’ portland cement concrete for pavement rehabilitation. Final Report, NCHRP Web Document 76, Transportation Research Board, National Research Council, Washington, DC; 2005.]. In the study fourteen different high-early strength portland cement concrete (PCC) full-depth repair mixtures (two replicates or batches were prepared for each mixture for a total of 28 batches) were designed for a 6–8h opening to traffic window. The fresh and hardened concrete properties, freeze-thaw durability and microstructural properties of the concrete were assessed as part of the laboratory testing program. As a result of this assessment it was determined that high-early strength PCC mixtures of adequate strength could be produced, but that interactions between the various constituents could result in durability problems in some mixtures, particularly those made with Type III cement and high-range water reducers. It is recommended that durability-related testing be conducted on such mixtures to ensure longevity of the repair.

Concrete specimens were obtained from an airport pavement that had been deiced with potassium acetate. A fraction of the coarse aggregate particles used in the concrete consisted of chert rich carbonate material. Some of these core specimens were cut into beams and immersed in either sodium hydroxide or potassium acetate solutions at elevated temperatures and expansion monitored. Thin sections were then prepared from the field concrete and from one of the beams immersed in the potassium acetate solution and one beam that had been immersed in the sodium hydroxide solution. These thin sections were examined with petrographic and scanning electron microscopes. Both beams exhibited pronounced Ca(OH)(2) depletion throughout the cement paste. These results were compared to the original concrete that had been subjected to potassium acetate during service. The original concrete did not exhibit pronounced Ca(OH)(2) depletion, but did show early signs of alkali silica reaction.

Many state highway agencies use various chemicals to deice or anti-ice pavement and bridge surfaces. Most often these are aqueous solutions of various chlorides (e.g., magnesium chloride, sodium chloride, and calcium chloride) or other chemicals such as calcium magnesium acetate, urea, or others. Possible detrimental effects to concrete caused by these chemicals have not been fully examined and documented. Mortar specimens of three different water-to-cement ratios (0.4, 0.5, and 0.6) were immersed in concentrated solutions of various chemical deicers and held above freezing at a constant temperature of 40°F up to 84 days. Considerable expansion and cracking were noted in specimens immersed in the MgCl2 and CaCl2 solutions. Petrographic analysis and quantitative microanalysis were used to positively identify the presence of Mg(OH)2 (brucite) formation in the outer layers of the specimens. Furthermore, the results presented clear evidence of calcium oxychloride formation in the specimens analyzed. Further research is being conducted, including the same immersion test at 40°F on portland cement concrete specimens, to identify whether this distress mechanism is of concern for structures such as roads and bridges when subjected to deicing chemicals containing CaCl2 or MgCl2.

Over the past 30 years, a great deal of research has been performed to develop an automated system to perform ASTM C 457, the standard test method for microscopical determination of parameters of the air void system in hardened concrete. The method presented here utilizes contrast-enhanced images created by filling the voids white and coloring the remainder of the hardened concrete surface black. The images were collected with a standard desktop flatbed scanner with an advertised optical resolution capability of 4,800 × 4,800 dpi (∼5.3 × 5.3 micron). Each image took approximately 10 min to collect. The “black and white” contrast-enhanced images were used in conjunction with knowledge of either the mix design or batch weights to perform the calculations set forth in ASTM C 457. Each analysis was accomplished in about 15 to 20 min using a computer script program on a standard personal computer. The same prepared surfaces were also analyzed with a commercially available air void system analyzer. The data collected from the commercial system correlated well with that from the flatbed scanner.

TiO2 nanotube semiconductors contain free spaces in their interior that can be filled with active materials such as chemical compounds, enzymes, and noble metals, giving them a fundamental advantage over colloids. Although the unique shape of semiconductor nanotubes makes them promising for a range of potential applications, significant developmental research is required. In this research, a novel TiO2 nanotube photocatalyst was prepared that has a p-n junction. The photocatalyst particle surface is physically divided into reduction and oxidation surfaces, which poses a potential driving force for the transport of photogenerated charge carriers. The structure of this nanotube catalyst was characterized using a scanning electron microscope (SEM) and X-ray diffraction (XRD). The catalyst activity was evaluated by coating the catalyst on HEPA filters and determining the destruction rate of toluene in air. The p-n junction nanotube catalyst was shown to have a much higher photocatalytic destruction rate than that of commercially available, nonnanotube structured material, and a higher destruction rate for nanotube catalysts that did not contain a p-n junction.

The chemical composition and morphology of alkali–silica reaction (ASR) products is of great importance in studying the reaction mechanism and assessing the effectiveness of mitigation techniques. Epoxy-impregnated, polished thin sections were prepared from an in-service concrete pavement to examine ASR products that originate from chert particles in the fine aggregate. Both hydrous and anhydrous thin-section preparation techniques were used to investigate the influence of sample preparation on the results. Two distinct morphologies of ASR products were observed in the voids adjacent to the chert particles: a bladed crystalline type and a glassy amorphous type. The chemical compositions of the reaction products were determined with a scanning electron microscope via quantitative X-ray energy dispersive spectrometry. Both the chemical composition and morphology were influenced by sample preparation, with hydrous preparation resulting in leaching and degradation. It is recommended that, when conducting studies to assess the ASR mechanism and the effectiveness of mitigation techniques, anhydrous sample preparation be used.