Ultra-high-performance concrete (UHPC) has progressively gained interest because of its favorable strength and durability properties. Considering applications of heat treatment and mass concrete, understanding the direct relationship between curing temperature and time is informative for construction decisions (such as formwork type and time of removal) to maximize performance per unit cost of UHPCs, as they can differ from conventional concrete. Limited datasets are currently available to ascertain the degree of change related to UHPC mechanical properties as a function of curing temperature and conditions. This study presents a systematic experimental program to investigate the effect of isothermal and submerged conditions on the rate and extent of compressive strength and elastic modulus development for UHPC, followed by development of numerical models that capture these effects with reasonable accuracy. Although the final elastic modulus appears to be unaffected by temperature, much higher compressive strength was achieved with higher curing temperatures compared to ambient conditions, and both properties were successfully modeled.

Self-consolidating concrete (SCC) is designed to fill any type of formwork and spread into place by its own weight in the absence of mechanical vibration. Due to the high flowability of SCC, it is more susceptible to suffer stability problems compared to conventional vibrated concrete. Dynamic segregation refers to segregation in concrete while being cast into a formwork or due to an impact or drop. In this paper, the main purpose is to understand how rheology governs dynamic segregation of SCC, explaining the effect of different mixture design parameters, by using the tilting box (T-box). Changes in admixture contents, paste volume, aggregate distribution, water-cementitious materials ratio (w/cm), and the width of the T-box have been investigated. The results show that dynamic segregation of SCC is dependent on the paste volume, the grain size distribution, fly ash content, and the width of the formwork, in addition to the rheological properties of the concrete.

Industry guidelines recommend that formwork be designed to withstand full hydrostatic pressures when using self-consolidating concrete (SCC) and highly flowable concrete. However, full hydrostatic pressures are seldom observed during SCC pours, meaning that it is possible to safely relax formwork design specifications. Numerous researchers have developed models that incorporate lab-tested material values to predict formwork pressure, but these models are affected by changing concrete mixture design, air temperature, humidity, and other factors that cannot be accounted for quickly. A simple field test method and model is presented in this study that predicts the formwork pressure using a calibrated behavior, which we call a “pressure decay signature.” The simple formwork pressure model is shown to agree well with experimentally measured values during the construction of two tall-walls, suggesting that this method and model can contribute to increased cost efficiency of SCC construction while maintaining safe practices.

The successful use of highly flowable self-consolidating concrete (SCC) containing recycled concrete aggregate (RCA) in structural applications entails proper assessment of lateral pressure developed on vertical formworks. Three series of relatively low to high stable SCC mixtures were considered in this paper; the virgin aggregates were substituted by 25, 50, 75, and 100% RCA. Regardless of SCC composition, test results have shown that mixtures prepared with increased RCA replacement levels led to reduced initial pressure measured after placement, as well as accelerated rates of pressure drop over time. The former phenomenon was related to higher RCA surface roughness that increases internal friction, while the latter was attributed to higher water absorption that improves concrete stability. A series of regression models based on thixotropy and relative water absorption of aggregates were developed to predict the effect of RCA on SCC formwork pressure.

Standard and nonstandard penetration-resistance tests were conducted on cement paste, mortars incorporating that paste, and concretes incorporating those mortars. Simultaneously, the diminishing ability to consolidate the concrete with a vibrator, impress a footprint into the concrete surface, manipulate that surface with a magnesium float, and otherwise deform the surface was recorded. The time at which freshly-placed concrete can no longer be effectively consolidated with an immersion vibrator, the time at which professional concrete finishers would begin hand- or power-floating of a concrete surface, and the limit of the capacity to deform concrete by adjusting formwork all occur significantly before mortar reaches “initial setting” as defined by ASTM C403. Likewise, the time at which a recently-cast concrete surface can no longer be manipulated by a hand float occurs well in advance of “final setting” as defined by ASTM C403.