This paper presents a model developed to predict the internal relative humidity (RH) of concrete during drying. The model makes use of simplified inputs, including the concrete mixture design and the cement Bogue composition, thus making it accessible to engineers and practitioners. These inputs are used to separately determine the permeability of both liquid and vapor phases, hence solving for moisture transport through an empirical derivation of the (de) sorption isotherm, total porosity, and pore tortuosity. The model is validated using previously published literature data as well as experiments designed specifically for model validation. The model was found successful in predicting RH profiles for the validation data with the simple inputs required. However, it was found that in cases where the standardized ASTM F2170 method is used to measure RH, the agreement between the model and experimental data decreases. This was found to be related to errors associated with performing humidity measurements within cavities drilled in concrete. Such errors are discussed, and room for improvement in in-place humidity measurements is proposed. Finally, the model is used to validate the use of RH measurements at a specific concrete depth to evaluate the susceptibility of moisture-sensitive flooring to failures.

This paper presents a real case study concerning the analysis of the cracking risk of a large reinforced concrete slab-on-ground with 9.84 in. (250 mm) of thickness and approximately 9257 ft2 (860 m2) of area. It was designed to prevent effects of severe environment conditions over the life span as thermal and drying shrinkage. This slab is a pool floor without expansion joint—jointless—to avoid leakage and early deterioration of the structure. The main properties were initially estimated based on the thermal structure behavior to evaluate the volume change effect from early ages to long-term effects. The proposed solutions to reduce the volume change effects of concrete were carried out in three parts: improvements in structural design; optimization of the concrete mixture; and adjustments in the construction process. After the concrete placement, the solutions proved to satisfactorily prevent cracks, thus ensuring proper performance of the pool.

An investigation was carried out on basalt fiber-reinforced concrete (BFRC) produced using various dosages of basalt fibers. The concrete mixture was designed with a target strength of 35 MPa (5075 psi), which is a typical strength for floor slabs and similar applications in which fiber reinforcement is often used. The concrete was tested for slump and air content in the fresh condition and for compressive strength, splitting tensile strength, flexural strength, and toughness in the hardened condition. Using these tests, the behavior of the BFRC was investigated and compared to fiber-reinforced concretes produced using similar dosages of polypropylene polyethylene synthetic fibers and crimped steel fibers. The basalt fibers were found to generally increase tensile and flexural strength (modulus of rupture), but were found to have very little effect on compressive strength and post-cracking behavior, and inspection found that the fibers had ruptured upon macrocracking.

Cracking and curling are two important problems in industrial concrete floors. In many practical cases, it is easier to design the concrete floor slab for mechanical loads than for shrinkage stresses. This paper proposes a simple equation that mirrors the major factors influencing the crack risk in concrete floor slabs. By using this equation, the industrial floor designer or contractor can make a proper material selection that leads to a substantially reduced crack risk. Tests on strength, free shrinkage, restrained shrinkage, and flexural creep support this hypothesis. Furthermore, the use of shrinkage-reducing admixtures (SRAs) seems to not only reduce the free shrinkage, but also maintains the beneficial condition of substantial creep that leads to shrinkage stress reduction.

The current study examines chemical and mechanical behaviors resulting from the gradual incorporation of incinerator fly ash (IFA) into an alkaline-activated coal fly ash (CFA) matrix, such as: 1) the incinerator ash is chemically stabilized; and 2) the resulting mixture provides fresh and hardened properties adequate for the production of commercially viable precast components. This paper presents the results of an extensive chemical characterization of IFA and CFA, including particle size distribution (PSD), X-ray fluorescence (XRF), and inductive coupled plasma (ICP) methods. Geopolymer concretes and grouts made from IFA, CFA, and four IFA-CFA blends were subjected to leachability tests, as well as extensive mechanical and rheological testing, including compressive strength, elastic modulus, Poisson’s ratio, and setting time. Preliminary results are encouraging, suggesting that toxicity levels of the leachate can be reduced by up to two orders of magnitude. Reduction in leaching levels of heavy metals was observed for Al, Cr, Ni, Zn, Se, Mo, Ba, Tl, Pb, and Th in geopolymer samples. Furthermore, the resulting mixture is workable and yields a mechanical strength of up to 41 MPa (6000 psi). PSD analysis showed CFA was 8% smaller than IFA. PSD plays a vital role in contributing to geopolymerization, as finer particle sizes involved in geopolymerization lead to a dense microstructure. This indicates that while geopolymerization could be viewed as an effective approach for treating IFA, immobilization of heavy metals by forming stable zeolites provides an additional mechanism for encapsulation of heavy metals. The use of IFA in beneficiation applications is expected to result in significant cost reduction to operators of municipal waste incinerators, eliminating costly transportation and landfill expenditures.