The sensitivity problem of polycarboxylate superplasticizers (PCEs) toward clay contaminants becomes more and more severe nowadays. The negative impact of clay contaminants, especially montmorillonite (MMT) on PCEs is stemming from the intercalation of polyethylene glycol side chains into the interlayer gallery of montmorillonite. In this study, two PCE polymers were synthesized from the same α-allyl ω-hydroxy poly (ethylene glycol) (APEG) macromonomer with designated side-chain lengths of 7 EO units, but different acids as co-monomers, namely, maleic anhydride (MA) and acrylic acid (AA). These two APEG PCEs were designed such as to possess the same anionic charge amounts and similar molecular weights. The dispersing performance of the two polymers was tested in the absence and presence of montmorillonite clay. It turned out that AA-7APEG exhibited much better clay tolerance as compared to that of MA-7APEG. To further investigate the interaction mode between PCEs and montmorillonite, XRD and adsorption measurements were carried out. Additionally, the Ca²⁺ binding capacity of the two PCE polymers was probed via charge titration experiments. The results show that MA-7APEG could chelate more calcium cations and thus lead to decreased anionic charge density and also reduced electrostatic repulsion towards MMT.

Polycarboxylates (PCEs) currently dominate the global superplasticizer market. Among them, HPEG and IPEG PCEs have attained a prominent position as they present the most cost-effective PCEs known at present. Recently, novel vinyl ether PCEs designated as EPEG and GPEG PCEs were introduced, thus broadening the family of VPEG PCEs, and their overall performance is still evaluated. Well documented are now the advantages of novel phosphated comb polymers which can significantly reduce the stickiness of concrete e.g. in UHPC. In spite of many attempts, so far no overall cost-effective clay tolerant superplasticizer has been identified, the challenge being that such a structure must include side chains that however do not contain polyethylene glycol/polypropylene glycol (PEG/PPG) or polyamines. Fortunately, for calcined clay blended cements, HPEG PCEs of specific molecular design as well as zwitterionic (amphoteric) PCEs have proven to be highly effective. Moreover, AAS binder systems were successfully fluidized with APEG or HPEG PCEs exhibiting particularly short side chains (nEO < 10). This review underlines the critical role that innovation in chemical admixtures will play in the future to facilitate a successful migration to low-carbon binders.

This paper presents a case study involving the structural analysis and design of an elevated foundation plinth to support multiple pieces of rotating machines with different operating weights and speeds. The equipment is used to operate a high-speed balancing testing facility for turbines and rotors that are located within an adjacent testing chamber. This project comprised of several layout and design challenges, including vibration and resonance concerns, effects of multiple operating frequencies, plinth shape, and pile foundation effects. Major concern was to maintain the high precision and strict tolerance limitations required by the high-speed balancing operations. Elevated machine foundations integral with other structures possess many natural frequencies, both locally and globally. The traditional design rules-of-thumb are not adequate for analyzing and designing elevated machine foundations. A computer-based finite element analysis method is required to identify the multiple natural frequencies of a complicated foundation structure. The strength design of a machine foundation can become very challenging when trying to implement code requirements that are mostly applicable to building elements and not to massive concrete foundations. This study recognizes the need for the development of a design standard to include special design requirements for mass concrete machine foundations.

Synopsis: Strain-hardening cement-based composites (SHCC) represent a special type of fiber reinforced concretes, whose post-elastic tensile behavior is characterized by the formation of multiple, fine cracks under increasing loading up to failure localization. The high inelastic deformability in the strain-hardening phase together with the high damage tolerance and energy dissipation capacity make SHCC promising for applications involving dynamic loading scenarios, such as earthquake, impact or blast.

However, the main constitutive phases of SHCC, i.e. matrix, fibers and interphase between them, are highly rate sensitive. Depending on the SHCC composition, the increase in loading rates can negatively alter the balanced micromechanical interactions, leading to a pronounced reduction in strain capacity. Thus, there is need for a detailed investigation of the strain rate sensitivity of SHCC at different levels of observation for enabling a targeted material design with respect to high loading rates.

The crack opening behavior is an essential material parameter for SHCC, since it defines to a large extent the tensile properties of the composite. In the paper at hand, the rate effects on the crack opening and fracture behavior of SHCC are analyzed based on quasi-static and impact tensile tests on notched specimens made of three different types of SHCC. Two SHCC consisted of a normal-strength cementitious matrix and were reinforced with polyvinyl-alcohol (PVA) and ultra-high molecular weight polyethylene (UHMWPE) fibers, respectively. The third type consisted of a high-strength cementitious matrix and UHMWPE fibers. The dynamic tests were performed in a split Hopkinson tension bar and enabled an accurate description of the crack opening behavior in terms of force-displacement relationships at displacement rates of up to 6 m/s (19.7 ft/s).

This paper presents the results of a study examining the effect of synthetic fibers on the flexural and shear behaviour of beams tested under quasi-static and blast loading. In total, ten beams built with normal-strength concrete and synthetic fibers are studied, with five specimens tested under quasi-static four-point bending and a companion set of five beams tested under simulated blast loads using a high-capacity shock-tube. Test parameters include the effect of concrete type (plain vs. fiber-reinforced concrete), fiber type (two types of macro-synthetic fibers) and transverse reinforcement (in plain and fiber-reinforced concrete beams). Under slowly applied loads, the provision of synthetic fibers is shown to improve the residual shear capacity of beams built without stirrups, while the combined use of synthetic fibers and stirrups is found to improve flexural ductility. The effect of synthetic fibers on blast capacity is examined by comparing the mid-span displacements, failure modes and damage of beams tested under gradually increasing blast pressures. The results show that the use of synthetic fibers increases the blast capacity of beams built without transverse reinforcement, delaying shear failure. When combined with stirrups the use of synthetic fibers is shown to enhance damage tolerance and allow for better control of residual mid-span displacements at equivalent blasts.