The use of plants as resources has been investigated to improve the quality of closed water areas. In this study, the strength properties of mortar containing reed ash are examined to utilize the inorganic components of reeds; furthermore, the improvement in flowability due to the addition of reed powder to mortar is investigated to utilize the organic components of reeds. The results confirm that mortar containing reed ash improves the strength in the long term, and that mortar containing reed powder improves flowability. However, it is observed that reed ash decreases the flowability of mortar, and that reed powder inhibits strength development. To address these issues, mortar is mixed with both reed powder and reed ash. The resulting mixture exhibits improved flowability when mortar is mixed with phenols, which results in long-term strength via pozzolanic reaction.
The hydration characteristics and mechanical properties of basic magnesium sulfate (BMS) cement containing steel slag (SS) are studied in the work. The heat release of the composite binders during hydration process was monitored, the phase compositions of hydration products were analyzed, the microstructures of hardened pastes were investigated, moreover, the compressive strength was tested. The results show that the hydration exothermic rate of BMS is slowed and the cumulative heat of BMS is suppressed by SS addition. The incorporation of SS leads to the formation of C-S-H, CaSO4•2H2O and Mg(OH)2, and suppresses the formation of 5-1-7 phase. Compared to plain BMS, the pore structure of the composite paste with SS addition is much coarser, the crystallization and growth of Mg(OH)2 lead to the occurrence of microcrack and large pores of the paste. The mechanical property of BMS is decreased by SS addition, especially when the content of SS addition reaches 20%, the compressive strength is significantly weakened in all tested ages.
The self-compacting geopolymer mortar (SCGM) is a new revolutionary concept in the construction industry. This study presents a summary of different influencing parameters that effect the compressive strength of SCGM. The test results showed that the water to geopolymer solid ratio (W/GPS), sodium hydroxide (NaOH) concentration, curing temperature, and curing rest period were the important parameters that had a significant impact compressive strength of SCGM. The increase in fly ash to sand ratio from 0.5 to 0.67 had a negative impact on the compressive strength of SCGM. The increase in curing temperature from 50°C to 80°C resulted in a continuous increase in the compressive strength of SCGM, however, its effect was much more significant at higher NaOH concentrations. Moreover, a contin-uous increase in the rest period before heat curing also had a negative impact on the compressive strength of SCGM. The increase in mixer speed resulted in an increase in compressive strength due to proper mixing of high viscosity SCGM paste. The 28 days compressive strength of more than 20 MPa with good flowability can be achieved for SCGM mix with W/GPS less than 0.349, NaOH molarity of 16 M, and cured at 50°C to 80°C without any rest period.
Alkali-activated slag (AAS) is a relatively new class of materials with superior properties to cementitious materials. Numerous factors affect the properties of AAS mixtures, and knowing the optimal levels of each factor can help in selecting the mix design that meets specific requirements. Optimizing AAS pastes based on the fresh and hardened properties and unit cost, then suggesting a model predict its properties has not been examined yet. In this study, the fresh and hardened properties of AAS paste were optimized using the full factorial design of experiments and response surface methodology (RSM). Effects of the main factors including the type and concentration of the alkaline solution (AS), modulus of sodium silicate (MSS), and sodium silicate (SS) to AS ratio on the properties of AAS pastes were studied experimentally. The results displayed that among the considered factors, the SS to AS ratio and type of AS have the most impact on the improvement of compressive strength of the mixtures. Finally, the optimized mixture was obtained based on maximum compressive strength and flowability while targeting the minimum cost. This mixture contained a NaOH alkaline activator with a concentration of 6 molars, MSS of 2.29, and SS to AS ratio of 0.4.
The Euler method of computational fluid dynamics (CFD), the Bingham constitutive relationship and the measured concrete performance indexes were combined as the basis, the horizontal coil test and super high-rise building pumping test of concrete were simulated by software FLUENT. The data of maximum pump pressure, pressure loss of horizontal pipe, pressure loss per horizontal bend, pressure loss of vertical pipe and pressure loss per vertical bend from the test and numerical model were analyzed comparatively. The results showed that the simulation models can promisingly describe the flow behavior of concrete during pumping. In addition, it was found that the thickness of the lubricating layer forming during the concrete flow in the pump pipe was about 2 mm. Finally, the velocity vector analysis of concrete flow in the pump pipe was elucidated. The velocity gradient of the lubrication layer decreased with the increase of the distance from the pump pipe inlet. The velocity gradient of the concrete in the yield layer raised continuously. The flow velocity of concrete in the plug layer boosted with the thickness of the plug layer abated gradually. The concrete tended to be stable after flowing about 6 m in the horizontal pipe.
In this study, we aim to investigate the interaction between alkali-silica reaction (ASR) expansion and multi-directional reinforced steel bars, and to clarify the weakening mechanism of bond performance under the influence of this interaction. First, a series of pullout specimens considering the influence of the steel bar diameter and stirrup number were prepared and then to different degrees of the accelerated ASR test to quantify the multi-directional restraint effect of the reinforced bars. After the accelerated ASR test, pullout tests were conducted to quantify the effect of ASR on the bond performance of the reinforced concrete. The test results show that uniform reinforcement results in a uniform expansion of concrete and a relatively small volumetric expansion rate. Moreover, the specimens without stirrups showed an increase in bond performance when the volumetric expansion rate was lower than 0.2%; however, the bond performance of some specimens with stirrups increased when the volumetric expansion rate was lower than 0.3% because the attenuation of bond performance was delayed by the stirrups. Finally, by comparing the analysis results and the experimental results, a chemo-mechanical analysis method coupled with an ASR expansion model and a poro-mechanical model was verified. This method can accurately predict ASR expansion, stress-strain state, and the bond damage caused by ASR.
The principal issue facing reinforced concrete (RC) structures is the cost of failure due to corrosion and aging of steel reinforcements. High-Ni weathering steel (WS) is presently one of the most viable materials seen to address this issue. It is considered a cheap alternative to heavily alloyed stainless steels and also offers significantly better corrosion resistance than carbon steels (CS). This paper reviews the history and development of high-Ni WS around the world. The authors traced in detail how its protective rust layer forms under aggressive marine atmosphere in comparison to conventional Cr-type WS and CS. Synthesis of multiple studies reveals their differences in terms of rusting mechanism, corrosion products, and microstructural characteristics. It became apparent, however, that there exists a vast gap in our understanding of high-Ni WS in the context of RC structures. Some of the unresolved issues identified from literature are: (1) compositional difference of rusts that form in atmosphere and concrete; (2) long-term behavior; (3) lack of parameters necessary for service-life prediction; and (4) required concrete conditions for rust development. Information derived from these research gaps will provide important insights for future development of high-Ni WS towards the end-goal of integrating it in concrete structures.