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Rapid freeze-thaw (F-T) tests were conducted to study the frost resistance of desert sand concrete (DSC) at different stress levels (SL), desert sand replacement rate (DSRR) and the number of F-T cycles. The impact of the SL, DSRR, and number of F-T cycles on the mass loss rate, ultrasonic wave velocity, and stress-strain curve of DSC was investigated through uniaxial compression tests. Scanning electron microscope (SEM) was used to examine the microstructure of DSC. The constitutive relationship was established considering the influence of the SL and number of F-T cycles. The results indicated that the frost resistance and uniaxial compressive mechanical properties of DSC could be effectively enhanced when desert sand was added at 40%. The peak strain initially decreased and then increased as the DSRR increased. In contrast, the peak stress first increased and reached a maximum value as the DSRR increasing to 40%, followed by a gradual decrease. The F-T cycles gradually deteriorated the macroscopic properties of DSC. The proposed constitutive model of DSC was established by combining the two classical models as the ascending and descending sections, respectively. The model prediction results matched well with the experimental results, which can provide a theoretical basis for the engineering application of DSC under F-T cycles and loading environments. [ABSTRACT FROM AUTHOR]

In order to study the compressive properties of desert sand concrete (DSC) after high temperature, desert sand was used to replace medium sand with replacement rate of 0%, 20%, 40%, 60%, 80% and 100% (by mass) to make DSC. The effects of fire temperature and desert sand replacement rate (DSRR) on the rebound value, ultrasonic velocity and compressive strength of DSC were analyzed. The grey prediction strength model of DSC after high temperature was established. Ultrasonic-rebound comprehensive method for measuring strength curve of DSC and formula of fire temperature were deduced. The results show that with the increase of fire temperature, the ignition loss rate of DSC increases gradually, specimen surface colour gradually changes from deep to shallow, and the compressive strength, rebound value, ultrasonic velocity of DSC increase first and then decrease. With the increase of DSRR, the rebound value and compressive strength of DSC increase first and then decrease. When DSRR is equal to 40%, the compressive strength and rebound value of DSC reach the maximum. The NSGM (1,3) model has excellent prediction performance with an average relative error of 8.6%, which can be used to predict the medium and long-term compressive strength of DSC after high temperature. The prediction accuracy of DSC ultrasonic-rebound comprehensive method for measuring strength curve meets the requirements of specification. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In order to make the coupling beam with small span-to-depth ratio meet the requirements in terms of bearing capacity, ductility and energy absorption, the fiber reinforced concrete (FRC) which shows excellent uniaxial tensile strain-hardening properties, cracks control ability and energy dissipation was introduced to cast the beam. The four diagonally reinforced FRC coupling beam specimens with small span-to-depth ratio and one diagonally reinforced common concrete beam were tested under reversed cyclic lateral loading. The specimens' failure process, failure modes, bearing capacity, deformation capacity and energy dissipation were studied. The results show that FRC can increase the bearing capacity, ductility and energy dissipation of the coupling beams, and the FRC coupling beams has a high shear capacity and deformation capacity, as well as good resistance to damage before the main diagonal cracks form, which can meet the needs of the bearing capacity and deformation under strong earthquakes and can continue to use without repair or with a little repair. [ABSTRACT FROM AUTHOR]