Durability of Concrete Subjected to the Combined Actions of Flexural Stress,Freeze-thaw Cycles and Bittern Solutions

Freeze-thaw durabilities of three types of concretesnormal portland cement concrete （OPC）, high strength concrete （HSC） and steel fiber reinforced high strength concrete （SFRHSC） were systemically investigated under the attacks of chemical solution, and combination of external flexural stress and chemical solution. Four kinds of bitterns from salt lakes in Sinkiang, Qinghai, Inner Mongolia and Tibet provinces of China were used as chemical attack solutions. The relative dynamic modulus （RDM） was used as an index for evaluating the damage degree during the course of chemical attack and stress corrosion. The experimental results show that the freeze-thaw durability of concrete is visibly reduced in the present of the flexural stress, i e, stress accelerates the damage process. In order to quantify the stress accelerated effect, a stress accelerating coefficient was proposed. The stress accelerating coefficient is closely related with the types of bitterns and the numbers of freeze-thaw cycles is. The more numbers of freeze-thaw cycles is, the greater the stress accelerating coefficient for various concretes will be. In addition, there also exists a critical ratio of external stress to the maximum flexural stress. If the stress ratio exceeds the critical one, the freeze-thaw durability of various concretes will be greatly decreased compared to the responding concretes without applied stress. The critical stress ratio of OPC, HSC and SFRHSC is 0.30, 0.40 and 0.40, respectively, indicating that HSC and SFRHSC have advantages over OPC and are suitable to use in the bittern erosion regions.

Non-equilibrium State Salt-forming Phase Diagram：Utilization of Bittern Resource in High Efficiency

Salt-forming regions for a complex salt-water system in non-equilibrium state of evaporation process are usually different from those in solubility diagrams.To understand the solid-forming region of NaCl and improve the utilization of bittern resources,experiments were carried out to evaporate 20 representative mixture solution samples of Na ^＋,Mg ^2＋ //Cl^-, SO4^2--H2O system with an average evaporation intensity of（1.4±0.4） g·L^-1 ·min^-1（water） at boiling temperature 348 K,and determine the NaCl solid-forming regions in non-equilibrium state.Because of the complexity of salt-forming region,a maximal region and a minimal region were proposed to express the non-equilibrium state salt-forming region with different crystal seed,and a conditional salt-forming region was proposed to present the characteristic region of non-equilibrium salt-forming phase diagram.The areas of the maximal and minimal regions are 2.00 and 1.56 times those in solubility diagram,so it is possible to utilize bittern resources in high efficiency.The recovery rates of NaCl were 99.65%,93.14%,88.57%,72.76%,and 83.68%for six typical bittern sources from Tulantai Salt Lake（China）,Dongtai Salt Lake（China） ,Jilantai Salt Lake（China）,Qarun Salt Lake（Egypt） and seawater,respectively.It is testified that the non-equilibrium state salt-forming phase diagram can be used in industrial processes.

Resistance to chemical attack of bittern-resisting cement in high-bittern environment

A new kind of bittern-resisting cement （BRC） was introduced. This material is based on the ternary cementitious system of clinker containing C4A3 S phase, high-activity ground granulated blast-furnace slag （GGBFS） and fly ash （FA）. The hydration process and the hydrated products of BRC were studied by means of XRD, TG-DTA and SEM, and the resistance to chemical attack of BRC in high-bittern environment was also examined. The corrosion experiment in seven kinds of brines proved that BRC exhibits an excellent resistance to chemical attack of bittern. The corrosion resistance factors were calculated and all of them were greater than 0.96. It showed that BRC totally controls the cement-based material corrosion in brines from four aspects： （1） making full use of the dominant complementation effect of mineral materials; （2） diminishing the hydrated products easy to be attacked; （3） improving the microstructure of hardened cement mortar; （4） degrading the chemical attack of bittern.

Extraction of High Purity Bischofite(MgCl_2·6H_2O) from Left Over-Resiudal Bittren,Lake Quroun,Egypt

1 Introduction The left-over(residual)brines often in industrial facilities is disposed back to the sea or in dump areas e.g.abundant salt mines in other cases.Dumping into the sea

Sea salt bittern-driven forward osmosis for nutrient recovery from black water: A dual waste-to-resource innovation via the osmotic membrane process

A dual“waste-to-resource”innovation in nutrient enrichment and recovery from domestic black water using a sea salt bittern(SSB)-driven forward osmosis(FO)process is proposed and demonstrated.The performance of SSB as a“waste-to-resource”draw solution for FO was first evaluated.A synthetic SSB-driven FO provided a water flux of25.67±3.36 L/m2 h,which was 1.5-1.7 times compared with synthetic seawater,1 M NaCl,and 1M MgCL.Slightly compromised performance regarding reverse solute selectivity was observed.In compensation,the enhanced reverse diffusion of Mg+suggested superior potential in terms of recovering nutrients in the form of struvite precipitation.The nutrient enrichment was performed using both the pre-filtered influent and effluent of a domestic septic tank.Over 80%of phosphate-P recovery was achieved from both low-and high-strength black water at a feed volume reduction up to 80%^90%.With an elevated feed pH(~9),approximately 60%-85%enriched phosphate-P was able to be recovered in the form of precipitated stuvite.Whereas the enrichment performance of total Kjeldahl nitrogen(TKN)largely differed depending on the strength of black water.Improved concentration factor(i.e.,3-folds)and retention(>60%)of TKN was obtained in the high-nutrient-strength black water at a feed volume reduction of 80%,in comparison with a weak TKN enrichment observed in low-strength black water.The results suggested a good potential for nutrient recovery based on this dual“waste-to-resource”FO system with proper management of membrane cleaning.