Matériaux et constructions

In this experimental investigation, synthetic macro fibers and conventional welded wire mesh (WWM) were used in composite slabs to investigate their effectiveness in controlling load and shrinkage induced cracking. Two types of experiments were conducted: restrained shrinkage tests and large-scale loaded composite continuous slabs. Both short and long-term performance was investigated. Shrinkage and load-induced crack widths, and mid-span deflection were measured. Different dosage rates of the synthetic macro fiber were used and compared with conventional WWM. The minimum dosage of fibers and conventional WWM specified by ANSI-SDI-C2011 to control cracking in composite slabs were particularly examined. The restrained shrinkage test provides data on crack width caused by shrinkage, while the large-scale continuous slab was intended to monitor the mid-span deflection and crack width across the middle support caused by the load, shrinkage and creep. The results show that both minimum WWM and fiber dosage have comparable performance in controlling the crack width. Long term monitoring indicate that the crack width for both reinforcing systems increased with loading time and stabilized thereafter. Finally, the mid-span deflections for both tested reinforcing systems indicate that the fibers have comparable performance to WWM both short- and long-term. The results of the long-term deflection and crack width relative to the short-term values show a significant and comparable time dependent increase in these properties for both reinforcing systems. Furthermore, no fracture in the crack bridging fibers was observed under sustained load. These results indicate that creep of composite slabs for both reinforcing systems is not entirely related to the type of reinforcing material bridging the crack.

This recommendation is based on the results of an inter-laboratory study organised by the RILEM technical committee TC 264-RAP "Asphalt Pavement Recycling"—Task Group 3 (TG3) focusing on Asphalt Binder for Recycled Asphalt Mixture. The TG3 aimed to evaluate the effect of a specific family of materials known as asphalt recycling agent (ARA) on the aged binder under different configurations. Even though ageing is an irreversible phenomenon, effective ARA must have the capability to improve the flexibility of the bituminous materials and their resistance against cracking susceptibility with no adverse effect on the rutting resistance of pavements containing reclaimed asphalt. A total of 17 participating laboratories analysed the properties of binder blends composed of aged binder from reclaimed asphalt in three different contents (60, 80, 100%), ARA and virgin binder. The physical properties of the blends were thoroughly evaluated through traditional and rheological binder testing. This recommendation proposes to restore the original material properties at low and intermediate temperatures (i.e. cracking resistance) while balancing the high-temperature characteristics (i.e. rutting susceptibility) with durable impact throughout the progression of ageing phenomena. Therefore, useing of the Dynamic Shear Rheometer is foreseen as a more suitable and sustainable means to evaluate binder blends containing an asphalt recycling agent. Compared with conventional testing, the proposed approach requires fewer materials while resulting in a faster experimental procedure with one single test.

Some problems of statistical control of concrete strength in non-destructive testing are considered. The procedures for rejection of gross errors and accounting for the actual law of concrete strength distribution are given. In the non-destructive control, the reliability and accuracy of a test result, fi, as well as the probability of a specified concrete strength, f′ c , should be the same as in testing with the use of a standard method (specimen testing). Proceeding from this concept, known acceptance criteria are analysed and those recommended by the author are described. The use of the latter permits a considerable reduction of the consumer's risk. Procedures for specifying a required average strength, f cr , are also analysed. In the use of the proposed acceptance criteria, the value of f cr may be reduced in many cases, and hence the cement content may be decreased.

In this paper, the nonmetallic powder recycled from waste printed circuit boards (PCBs) is used in cement mortar as admixture. The mechanical properties, bulk density, air content, water-retention property, shrinkage rate and water capillary adsorption are tested. The results show that the waste PCBs nonmetallic powder causes an increase in air content and improves the water-retention property of fresh mortar, decreases the bulk density of hardened mortar. The compressive strength and flexural strength of mortar with PCBs nonmetallic powder change slightly with the m p/m c below 15%. The tensile bond strength goes down continuously with the increase of the m p/m c but the reducing trend in the m p/m c range from 0 to 10% is slow. The drying shrinkage rate of mortar has little change as the m p/m c varies from 0 to 15%. The water capillary adsorption of mortar with the m p/m c of 5, 10 and 15% are lower than that of control. Cement mortar made with recycled waste PCBs nonmetallic powder is a new type of green building materials, which is friendly to environment and has broad application prospects.

The pore structure of concrete has long been recognized as the key to a wide range of different mechanical, physical and chemical properties. However, the finite range of the different interrogation techniques for measuring pore structure has always limited our overall picture. In order to add to that picture, a high resolution, three-dimensional imaging technique called x-ray microtomography was employed as a way to link measurable microstructural features with alternate measurements of permeability in different concrete systems. Four different concretes were imaged at spatial resolutions between 1 and 4 microns. Using 3D image analysis techniques, the pore system was characterized by size distribution and connectivity. A parameter we termed “disconnected pore distance” correlated well with standard measures of chloride permeability.