Early-Age Evolution of Strength, Stiffness, and Non-Aging Creep of Concretes: Experimental Characterization and Correlation Analysis

Six different concretes are characterized during material ages between 1 and 28 days. Standard tests regarding strength and stiffness are performed 1, 3, 7, 14, and 28 days after production. Innovative three-minute-long creep tests are repeated hourly during material ages between one and seven days. The results from the standard tests are used to assess and to improve formulas of the fib Model Code 2010: the correlation formula between the 28-day values of the strength and the stiffness, and the evolution formulas describing the early-age evolution of the strength and the stiffness during the first four weeks after production. The results from the innovative tests are used to develop a correlation formula between the 28-day values of Young’s modulus and the creep modulus, and an evolution formula describing the early-age evolution of the creep modulus during the first four weeks after production. Particularly, the analyzed CEM I concretes develop stiffness and strength significantly faster than described by the formulas of the Model Code. The creep modulus of the investigated concretes evolves significantly slower than their strength and stiffness. Thus, concrete loaded at early ages is surprisingly creep active, even if the material appears to be quite mature in terms of its strength and stiffness.

Microstructure and Relative Humidity Effects on Long-Term Indentation Creep Properties of Calcium Carbonate Cement

This paper addresses the effect of both microstructure and relative humidity on the long-term creep properties of sustainable calcium carbonate (CaCO3) cements. Those can be prepared by mixing amorphous calcium carbonate and vaterite with water. A larger starting amount of vaterite, XV, within the mixture design gives a higher elasticity and resistance to the specimens due to the larger overall bridging area within the newly formed calcite crystals. Regarding creep properties for a given relative humidity, the amplitude of creep strain decreases with XV, and makes the relation between the elastic modulus, E, and hardness, H, of the samples to be linear with the contact creep modulus, C. On the other hand, for a given composition, the amplitude of creep increases with the relative humidity, making the contact creep modulus, Ci, to rise exponentially with the elastic modulus, E, and hardness, H, of the specimens. The most probable creep mechanisms for this kind of cement seem to be a combination of microcraking in the early stages and dissolution and reprecipitation of calcite in the long-term (also known as pressure solution theory). The presence of water in pores with increasing relative humidity might enhance the local dissolution of calcite, and hence the creep amplitude.

EFFECTS OF SHORT TERM AGING ON DYNAMIC CREEP PROPERTIES OF ASPHALT MIXTURES

Many factors affect pavement service life. Aging as one of these factors occurs due to binder volatilization and oxidation. Aging increases binder viscosity and subsequently results in stiffer mixtures. Transportation of asphalt mixture from plant to field may cause variations in the levels of aging. This study attempts to determine the effects of aging on mixture permanent deformation or rutting during transportation from plant to field and to simulate the aging conditions in the laboratory. The rutting parameters evaluated include creep stiffness, cumulative strain, creep modulus and creep rates of mixtures collected from plant, field and samples artificially produced in the laboratory. The results showed that temperature increment significantly changed mixtures rutting properties, while aging during mixture transportation from plant to field has no effect on rutting. It was also found that artificially aging the mixtures by varying aging duration that conducted for this study, cannot exactly simulate the plant and field aging conditions.

Compatibilization of Thermoplastic Polyurethane and Polypropylene with a SEBS Compatibilizer

The effect of styrene-ethylene/buthylene-styrene triblock copolymer (SEBS) on the thermal and rheological properties of thermoplastic polyurethane/polypropylene (TPU/PP) blends was investigated. For the selection of polymer materials and polymer blends for various fields of applications the stability of materials under constant deformation are very important. The blends were therefore characterized by measuring secondary viscoelastic functions creep, recovery and creep modulus using dynamic mechanical analysis (DMA) in the creep fatigue regime. The master curves at the reference temperature of 25°C were created by time-temperature correspondence (TTC) principle. The correlation of the creep modulus with time, temperature and addition of compatibilizer was discussed. The differential scanning calorimetry (DSC) results indicated that the addition of SEBS as a compatibilizer in TPU/PP blends increases glass transition temperature (Tg) and decreases crystallinity (χc). SEBS block copolymer acts as an efficient compatibilizer for TPU/PP blends.