Experimental research on mechanical properties of desert sand steel-PVA fiber engineered cementitious composites

An orthogonal experimental design method involving five-factor and four-level is adopted for the mix design of Desert Sand Steel-PVA fiber ECC. The effect of each level on Mechanical properties of ECC and the difference of Mechanical properties between each level is analyzed. The influence of different experimental factors is discussed, which includes water-binder ratio, fly ash substitution rate, desert sand substitution rate, proportion of PVA fiber and proportion of steel fiber. The experimental results indicate that water-binder ratio and fly ash substitution rate are the most principal and significant influencing factors on the compressive strength of ECC, regardless of age. Steel fiber is conducive to development of splitting tensile strength; PVA fiber is conducive to the development of flexural strength. High strength ECC can be prepared when the desert sand substitution rate is high. As the raw material of ECC, river sand can be 90% replaced by desert sand

Enhanced ductility and toughness of desert sand engineered cementitious composites

Economical desert sand engineered cementitious composites (DS-ECCs) using a mixture of cement, fly ash, local desert sand, water, low-cost PVA fibers, and chemical additives were developed, aiming for a further enhancement in ductility and toughness. The mechanical behavior of DS-ECCs for two sand samples (from Mu Us and Tengger deserts, China) was determined using uniaxial tension/compression tests and three-/four-point bending tests. The results showed that desert sand-based ECCs with the designed mix ratios had better mechanical properties than the river sand-based ones. Compared with the river sand-based ECCs at 28 and 56 day, the DS-ECCs presented superior ultimate tensile and comparable compression strengths. The excellent ductility was characterized by ultimate tensile and compression strains of 3–7% and over 1%, respectively. Meanwhile, the DS-ECCs showed improved flexural properties with outstanding fracture and bending strengths (4–9 kN and 21–30 kN) and toughness. The findings of this study will further strengthen the mechanical performance of DS-ECCs and broaden their engineering applicability

The bonding performance of desert sand self-compacting concrete overlay on normal strength concrete substrate : Macro, micro, and ultrasonic testing

This study investigates the performance of concrete containing desert sand (desert sand concrete and desert sand self-compacting concrete) as overlay concrete to bond with normal-strength concrete substrate, with different bonding interfaces being considered. The impermeability of the bonding interface is determined by the electrical resistance test. Static bonding strength is tested by conventional mechanical tests. The dynamic properties of bonded specimens are also studied by dynamic response tests. Non-linear parameters, low-frequency energy parameters and ultrasonic velocity are included in the bonding interface ultrasound detection. The microstructural and chemical compositional of the overlay transition zone (OTZ) are analysed to reveal the mechanisms of bonding behaviour. The results indicate that the interface electrical resistance is positively related to bonding strength. Using concrete containing desert sand as the overlay concrete improves bonding interface adhesion for 30 % at most. Bonding performance can be affected by the interface pattern and volume density in both static and dynamic conditions. The bonding strength and damping ratio with properly treated interfaces can be increased by over 300 % and 38 % than those of untreated groups, respectively. The dynamic response of the bonded specimens can effectively reflect the bonding performance. The non-linear ultrasound method and the ultrasound energy method are more accurate and sensitive than traditional way (ultrasonic velocities) in detecting the bonding interface. The incorporation of desert sand in the concrete or lowering W/B considerably contributes to a series of benefits to the microstructure of the bonding interface. The bonding gap width is reduced by 17 % and 72 % for DS incorporation and lower W/B, respectively. Characterized by Ca/Si, the OTZ width is reduced by 10 % and 31 % for DS incorporation and lower W/B, respectively. Characterized by micro-hardness, the OTZ width is reduced by 21 % and 24 % for DS incorporation and lower W/B, respectively, which provides an important reference for the engineering application of desert sand self-compacting concrete

Study on Bond Performance between Corroded Deformed Steel Bar and DS-ECC

In order to study the bond performance between desert sands engineered cementitious composites (DS-ECC) and corrosion steel bars, seven groups of specimens were designed and manufactured. Through the center pull-out test, the effects of different types of desert sands, the rate of corrosion (0, 5, 10 and 15%), and the anchorage length of steel bars (5d and 8d) on the bonding properties of DS-ECC and corrosion steel bars were studied. Moreover, a de-rusting agent was used to remove the corrosion, and three groups of specimens were pulled out from the center of the de-rusted steel bars. The results showed that both Tengger DS-ECC and Mu Us DS-ECC have good bond properties with corrosion steel bars. The bond stress slip curves between DS-ECC and corrosion steel bars can be divided into four stages: the micro-slip, slip stage, failure stage and residual stage. The bond stress slip curves between DS-ECC and de-rusted steel bars can be divided into the micro-slip stage, failure stage and residual stage, and splitting and pulling-out failure occurs in DS-ECC specimens. The ultimate bond strength is the highest when the corrosion rate is 5%. The bond toughness index is positively correlated with the anchorage length of steel bars, and negatively correlated with the corrosion rate of steel bars. According to the test results, the bond–slip mathematical relationship is established

Disaster Prevention and Mitigation Index Assessment of Green Buildings Based on the Fuzzy Analytic Hierarchy Process

Assessment systems for green buildings around the world have been developed over many years, but there is a lack of assessment elements for the disaster prevention and mitigation (DPM) capabilities of green buildings in many indicators. DPM indexes based on the four main aspects of structural safety, DPM design, facility settings, and resource utilization are proposed here with consideration to the complex natural disasters that occur in China (fires, earthquakes, floods, etc.) and relevant codes. Then, an assessment system for the DPM indexes of green buildings is established by the fuzzy analytic hierarchy process (FAHP) in order to evaluate the DPM ability of green buildings and to quantify the impact of different indexes on the DPM ability of green buildings; this system is also used to evaluate and compare DPM capability suggestions, taking two green buildings in South and North China as examples. The results show that the DPM capacities of the two green buildings were evaluated as good, but that the scores for the site planning and water-saving systems of the green building in South China were significantly lower—meaning that measures such as optimizing drainage systems, managing stormwater runoff, permeable paving, rainwater gardens, and installing rainwater harvesting equipment should be implemented. Then, the theory of the utilization rate of DPM conversion is put forward, providing a reference for the future development of green building DPM index systems

Mechanical Properties of Desert Sand-Based Fiber Reinforced Concrete (DS-FRC)

This paper presents the study on the properties of high-ductility fiber reinforced concrete made with desert sand from China’s Mu Us desert. The workability and uniaxial tensile/compression properties of undisturbed desert sand-based fiber reinforced concrete (DS-FRC) with the change of water-to-binder ratio (W/B), sand-to-binder ratio (S/B) and desert sand replacement rate (DSRR) were experimentally investigated. Experimental results reveal that the appropriate W/B and desert sand content are conducive to the workability development of DS-FRC. The uniaxial tension/compression properties of DS-FRC are mainly affected by the W/B. Especially, the highest uniaxial tensile/compression stresses and corresponding strains are obtained at the W/B of 0.29. The S/B has similar effects on the uniaxial tensile/compression properties, and an S/B of 0.36 is the optimal ratio. In terms of the DSRR, it shows less effect on the uniaxial tensile/compression properties, even for the DSRR of 100%. The results of the tests indicate that undisturbed desert sand can be used as silica sand in high-ductility fiber reinforced concrete

Enhanced Ductility and Toughness of Desert Sand Engineered Cementitious Composites

Economical desert sand engineered cementitious composites (DS-ECCs) using a mixture of cement, fly ash, local desert sand, water, low-cost PVA fibers, and chemical additives were developed, aiming for a further enhancement in ductility and toughness. The mechanical behavior of DS-ECCs for two sand samples (from Mu Us and Tengger deserts, China) was determined using uniaxial tension/compression tests and three-/four-point bending tests. The results showed that desert sand-based ECCs with the designed mix ratios had better mechanical properties than the river sand-based ones. Compared with the river sand-based ECCs at 28 and 56 day, the DS-ECCs presented superior ultimate tensile and comparable compression strengths. The excellent ductility was characterized by ultimate tensile and compression strains of 3–7% and over 1%, respectively. Meanwhile, the DS-ECCs showed improved flexural properties with outstanding fracture and bending strengths (4–9 kN and 21–30 kN) and toughness. The findings of this study will further strengthen the mechanical performance of DS-ECCs and broaden their engineering applicability

Frost Resistance of Desert Sand Concrete

Demand for medium sand has increased greatly with increasing infrastructure construction items. The shortage of construction sand resources has become a serious problem in many districts. It not only increases the engineering cost, and the overexploitation of river sand and mountain as medium sand also brings a series of serious environment problems. There are abundant desert sand (DS) resources in western China. If DS resources can be used to substitute medium sand to produce desert sand concrete (DSC), which was suitable for engineering practice, the environment can be improved and engineering cost can be reduced. Although many researchers had focused on the mechanical performance of DSC, there were few documents on the frost resistance of DSC. Frost resistance experiments of DSC with 50% desert sand replacement ratio (DSRR) and ordinary concrete (OC) were performed in this paper. Influence of freeze-thaw cycles on the mechanical properties of OC and DSC was analyzed. Experimental results showed that, with increasing freeze-thaw cycles, the damage, peak strain, and porosity increased, while elastic modulus, Poisson's ratio, and peak stress declined, the stress-strain curves tended to be flat. Under the same condition of freeze-thaw cycles, the frost resistance of DSC with 50% DSRR was higher than that of OC. Constitutive model of DSC after different freeze-thaw cycles was formulated. The results predicted by constitutive model agreed well with experimental results, which can provide technical support for DSC engineering practice

Study on freeze-thaw resistance with NaCl of desert sand engineering cement composites

To test the salt-freezing resistance performance of desert sand engineering cement composite (DSECC) prepared by different types of desert sand, the specimens with 3% NaCl solution on the top surface after 56 days of curing were tested by one-sided freeze-thaw cycles (FTC) and compression test after freezing and thawing. Two desert sands were collected from the Tengger Desert and Mu Us Desert in China, denoted T and M. The appearance, water absorption rate, mass loss rate, relative dynamic elastic modulus and longitudinal ultrasonic speed of the DSECC were tested after 0, 4, 8, 12, 16, 20, 24 and 28 cycles of freeze-thaw. Compressive strength was tasted after 8, 16, 24, and 32 cycles of freeze-thaw. Results show that FTC can accelerate the damage of the appearance. Meanwhile, the water absorption rate increases, the relative dynamic elastic modulus, the longitudinal ultrasonic wave speed, and the compressive strength decreases. Under the same FTC, the salt-freezing resistance performance of DSECC using T has slightly better than that using M

Effect of desert sand on the uniaxial compressive properties of mortar after elevated temperature

In China, medium sand is widely used for engineering applications. However, over quarrying of medium sand to meet the demand for urbanization has led to the environmental issue. The arid area of Northwest China, which has high concentration of desert could provide sufficient supply of desert sand for engineering applications. In this paper, desert sand was used to replace medium sand to produce desert sand mortar (DSM). The uniaxial compression test was performed on the DSM undergoing elevated temperature treatment, and the stress-strain curves of the DSM after different temperatures were obtained. The effects of temperature and desert sand replacement rate (DSR) on the peak stress, peak strain, elastic modulus, Poisson's ratio, and mass loss rate of DSM was analysed. The test results showed that with the increase of DSR, the peak stress and elastic modulus of DSM first increased and then decreased. As the temperature increased, the Poisson's ratio of the DSM decreased first and then increased. Based on regression analysis, the relationships between peak stress, peak strain, elastic modulus, Poisson's ratio of DSM, temperature, and DSR were obtained. At the same time, a one-parameter compression constitutive equation of DSM after the elevated temperature was established. Since the equation has only one parameter, the calculation process was greatly simplified based on ensuring the calculation results. The model was in high agreement with the test results. This equation can provide a reference for further studies in the field of mechanical properties of DSM and desert sand concrete (DSC) after elevated temperatures