In countries with severe climate, in winter period ready-mix concrete is exposed to cooling down during transportation and placing before heat impact. To eliminate negative influence of negative temperatures, antifreeze admixtures are used purposely. Russian Standard GOST 24211-2008 stipulates antifreeze admixtures performance testing both at short negative temperature exposure (so called “warm” concrete) and for permanent hardening at temperatures below zero. In both cases the only performance criteria is concrete compressive strength. On the other side, in European standards such tests are not provided as a rule.

Statistically, nowadays antifreeze admixtures are used in very low dosage (~2÷3% of liquid commercial products for up to -25°С for “cold” concrete and even less for “warm” concrete technology). It was established, that, while using such amount of antifreeze admixtures, even short term exposure to negative temperatures (without concrete freezing) can adversely effects concrete`s water permeability. On examples on set of concretes with different dosages of common antifreeze admixture (up to maximum level recommended by “Temporary Construction Standards” 46-96 for -5÷-15°С range), main factors that influence on water permeability of concretes hardened under negative temperatures were observed. The formation of a fine microstructure due to the pozzolanic additive increases the resistance of the concrete to freezing, but the stability of the concrete water permeability can be achieved only by ensuring near-zero ice formation in the pore liquid.

ACI 437 provides requirements for the performance of large scale structural load tests. These include mapping and monitoring cracks, shoring, and actual application of the load in a minimum of four separate increments. Any walls or other improvements that might provide support to the element being evaluated must be cut free. Deflection is to be monitored and load deflection curves prepared for each increment, and the full load is to remain in place for a minimum of 24 hours. Straightforward as these requirements appear, they can present a daunting task for those actually conducting the test. Where reaction is available for simple tests such as for beams and girders, either hydraulic jacks or pneumatic bags can be used to supply the load. Where large horizontal areas such as floors are involved, such simplicity is often not possible and some form of physical mass must be used. In areas that are open, the load can be applied with a crane, but on the interior of structures it must often be applied by hand or with the aid of small handling equipment, which severely limits the choice of load media. Whereas load tests are usually designed by structural engineers, the actual application is performed by construction workers. In order to assure optimal performance, it is imperative that both work together during the design as well as the application. The schedule and logistics of the loading operation must be well thought out prior to the actual work. Obviously, safety of the overall operation must be assured. Consideration must be given to not only the potential failure of the element being evaluated, but damage to other portions of the structure as well. This can include overloading of other elements during movement and handling of the load media, or damage by flooding where water is used. The logistics of load tests are discussed in detail, including preloading surveys and documentation, provision of shoring and other required preparation of the test area, selection of the load media and its application, and the required monitoring and control.

The construction of submerged or partially submerged pile caps often requires the use of a cast-in-place unreinforced slab referred to as a seal slab. This slab is cast underwater around piling and inside sheet pile walls to form the bottom of a cofferdam and withstand upward hydrostatic pressure. As the seal slab is only used for a relatively short period of time during placement of the reinforcing steel and concreting, its design has received little attention in refinement tending toward conservatism. Therein, the magnitude of available bond strength between the seal slab and piling to resist the uplift pressure has been poorly quantified and largely underutilized. This paper presents experimental results from 32 full-scale tests conducted to define the interface bond between cast-in-place concrete seal slabs and piling (sixteen 356 mm square prestressed concrete piles and sixteen 356 mm deep steel H-piles). Three different concrete placement environments--dry, fresh water, and bentonite slurry--were evaluated using the dry environment (where no fluid had to be displaced by the concrete) as the control. The effective seal slab thickness was varied between 0.5d and 2d, where d was either the width or depth of the pile section. Both "soil-caked" and normal, clean pile surfaces were investigated. Additionally, four of the sixteen concrete piles were cast with embedded gages located at the top, middle and bottom of the interface region to define the shear distribution. The study showed that: (1) significant bond stresses developed even for the worst placement environment, and (2) the entire embedded surface area should not be used in calculating the pile-to-seal slab bond capacity. Current design values in the Florida Department of Transportation specifications reflect the findings of this study.

This paper reports on the experimentally and analytically observed behavior of unbounded post-tensioned precast concrete walls under static monotonic and cyclic lateral loads. Results show that the limit states that characterize that lateral load behavior of the walls occur as anticipated in the design of the walls and at force and drift levels predicted by the analytical model, except that the experimentally observed drift capacity exceeds the drift capacity predicted by the analytical model. Cyclic lateral load results how that unbonded post-tensioned precast walls can undergo significant nonlinear lateral drift without significant damage, and can maintain their ability to self-center, thus eliminating residual lateral drift.

Axial compression test results for square RC columns incorporation Taiwanese construction practice in the placement of stirrups and various kinds of jacketing schemes are presented. The jacketing schemes include circular, octagonal and square shapes. The jacketing materials vary from stell plate to carbon fiber reinforced polymer (CFRP) COMPOSITES. It is found from the monotonic axial load test results that the failure mode of the benchmark non-retrofitted specimen is identical to that observed in real damage cases subsequent to the 1999 Chi-Chi Taiwan earthquake. The benchmark specimen developed its design strength but a non-ductile failure mode occurred soon after the peak load was reached. Among the retrofitted specimens, the steel jacketed specimens exhibit not only greatly enhanced load carrying capacity but also excellent ductility performance. Test results show that CFRP sheets are effective in increasing the column axial strength, but the sheets could fracture suddenly in high strain conditions due to their brittle material characteristics. Test results indicate that CFRP sheet wrapping in general is not as effective as steel jacketing in improving the axial ductility capacity of RC columsn. However, the proposed octagon-shaped CFRP wrapping scheme exhibits an improved performance compared to rectangular-wrapped columns using the same layers of CFRP sheets. Tests confirm that all octagonal stell or CFRP jacketed specimens have axial load capacities more that 2 time the nominal capacity.