Yong Yu

Most studies of adding superabsorbent polymers (SAP) into concrete focus on high‐strength concrete, while this paper aims to understand the influence of SAP on “ordinary concrete” at a w/c ratio being 0.4 or 0.5. The proposed experiments include the effect of particle size, mixing methods, and dosages on the restrained shrinkage and mechanical properties of mortar and concrete. Mortar with varying dosages of SAP (0.1, 0.2, and 0.3 wt.%) and two types of SAP (type‐a of 30–60 mesh and type‐d of 300–400 mesh) was studied to evaluate the effect of SAP on mortar's cracking and strength. Two mixing processes of SAP (dry and pre‐wetted) were used to examine the effect of SAP on the mortar's shrinkage and mechanical properties. Furthermore, concrete specimens with a w/c ratio of 0.5 were prepared to investigate the cracking performance of concrete using the restrained squared concentric ring test method, a new approach which can predict the cracks location and pattern to evaluate the restrained shrinkage of concrete. The result revealed that the addition of SAP in a prewetted state decreased the mechanical properties at early curing age. The addition of 0.3 wt.% SAP was found to have mitigated the restrained shrinkage while prolonging the time to cracking of cementitious composites. The major finding is that adding SAP to ordinary concrete reduces shrinkage and improves mechanical strength, which should be further looked into and explored in its application in engineering work.

Three‐Mile‐River Bridge is located in Lu‐shan County, Henan, China. The bridge length is 80 m and width is 17.25 m with the deck thickness being 0.3 m. The deck construction is finished in June 2018, which consumed 200 cubic meter of crumb rubber concrete (CRC) with added super‐absorbent polymer (SAP), and opens for traffic in July 2018. This is the first case of SAP‐CRC bridge deck reported to the public with “pump concrete” technical being employed. The scanning of SAP‐CRC samples taken from the job site shows that rubber crumbs are largely uniformly distributed. The free restrained test on SAP‐CRC concrete and the test of restrained externally squared eccentric ring experiment on the mortar specimens made by filtering 10 mm coarse crumbs out of paving concrete show that SAP‐CRC exhibits an improved property in shrinkage behavior and cracking resistance. The original deck design is a three‐layer configuration: 0.3 m concrete + water approval sealing + 0.03 m hot mix asphalt. Consider CRC's excellence in preventing cracking, the sealing, and hot mix asphalt is removed, which results in a 10% reduction in construction cost and time. It is a technical success to add SAP into fresh CRC to suppress so called “rubber particle up‐floating phenomenon,” as well as an engineering/commercial success in the sense that this deck project is implemented following common practices of commercial construction operation and cost‐saving, which sets an case study to future similar applications that potentially will consume large quantity, if not all, of recycled rubbers from scrap tires worldwide.

Understanding the dynamic behavior of Lightweight Aggregate Self‐Compacting Concrete (LWASCC) is of importance to the safety of concrete structures serving in dynamic loading conditions. In this study, the fundamental dynamic properties of LWASCC with three types of LWA were investigated by the impact resonance method. Results show that the dynamic elastic and shear modulus generally decrease with the increase of LWA volume fraction, whereas three types of LWA exert limited influence on dynamic Poisson’s ratio. The dynamic elastic and shear modulus show good linear dependence upon compressive strength. The inclusion of three types of LWA significantly increases the damping ratio, indicating significantly enhanced damping capacity of LWASCC under dynamic loading conditions. The damping ratio of LWASCC is improved by 2.0%, 4.4%, and 2.9% when adding 1% (by volume) expanded clay, rubber, and expanded polystyrene, respectively. The compressive strength and dynamic performances of LWASCC are highly influenced by the intrinsic properties (elastic modulus, damping capacity, wettability, etc.) and geometrical characteristics (size, surface roughness, etc.) of LWA, as well as the LWA‐matrix bonding capacity.

Cracks greatly impact the durability of concrete structures due to their influence on the migration of chloride ions and the corrosion process of steel bars. This study investigates the effects of transverse cracks on chloride diffusion and the corrosion behavior of two types of steel bars (low carbon steel and corrosion resistant steel) in fly ash concrete with 1 kg/m³ solution-polymerized super absorbent polymer. Electrochemical impedance spectroscopy was used to monitor the chloride-induced corrosion behavior of steel bars in concrete. The chloride profile around cracks was tested via chemical titration. The corrosion products diffusion area was photographed and measured to evaluate the influences of cracks on the corrosion degree of steel bars. Transverse cracks greatly influence the chloride ion transport. When their width is less than 0.15 mm, cracks exert little influence on both chloride diffusion and steel corrosion. When the crack width exceeds 0.15 mm, the chloride ion transmission coefficient is significantly improved and steel corrosion is accelerated. However, when the crack width exceeds 0.20 mm, this effect is gradually weakened. Based on the experimental data, a quantitative relationship between the crack width and the chloride ion transmission coefficient in electric acceleration was established.