Effect of internal curing by using superabsorbent polymers (SAP) on autogenous shrinkage and other properties of a high-performance fine-grained concrete: results of a RILEM round-robin test

The article presents the results of a round-robin test performed by 13 international research groups (representing fifteen institutions) in the framework of the activities of the RILEM Technical Committee 225-SAP “Applications of Superabsorbent Polymers in Concrete Construction”. Two commercially available SAP materials were used for internal curing of a high-performance, fine-grained concrete in combination with the addition of extra water. The concrete had the same mix composition in all laboratories involved but was composed of local materials. All found a considerable decrease in autogenous shrinkage attributable to internal curing. Also, with regard to the shrinkage-mitigating effect of both particular SAP materials, the results were consistent. This demonstrates that internal curing using SAP is a robust approach, working independently of some variations in the concretes’ raw materials, production process, or measuring technique. Furthermore, the effects of internal curing on other properties of concrete in its fresh and hardened states were investigated. These are consistent as well and expand considerably the existing data basis on properties of concrete materials containing SAP.     

Untersuchung zur Ringöffnungspolymerisation von 2-Phenoxymethyl-1,4,6-trioxa-spiro-[4,4]-nonan

Investigation of Ring-Opening Polymerization of 2-Phenoxymethyl-1,4,6-trioxa-spiro[4,4]-nonan Under the conditions of a radical induced cationic ringopening-polymerization the spiro ortho ester 1b can be polymerized with diphenyliodoniumtetrafluorborat/benzpinacol (1:1). The optimal initiator concentration is 2–2.5 mol-% Ph₂I⁺BF₄⁻. The average molecular weight is 6000, Tg = −4°C. Polymerization of 1b in presence of BF₃ · Et₂O produced identical results. The structure of polymer 2b was indicated by its analysis as well as its infrared spectra.     

New Starch Phosphate Carbamides of High Swelling Ability: Synthesis and Characterization

The paper describes the synthesis of starch phosphate carbamides by reacting starch with phosphoric acid and urea. A solid state technique in vacuum at elevated temperatures is used. The degree of substitution of phosphate (DS_P) and carbamide groups (DS_C) can be adjusted by the molar ratio of starch: phosphoric acid: urea, the reaction temperature, and time. The starch derivatives prepared show remarkable swelling if the DS_P ranges between 0.2 and 0.3. With increasing content of urea in the reaction mixture the water‐holding ability is still significantly improved, which is explained by chemically and especially physically introduced urea into the starch polymer. Furthermore, the ratio of amylose: amylopectin of the starch samples influences both the DS values and the physicochemical properties, e.g., swelling power and multivalent metal ion adsorption of the products. The structure of the new polymers was determined by means of FTIR, ¹³C‐ and ³¹P NMR spectroscopy as well as by gel permeation chromatography (GPC).     

Non-oxide CMC fabricated by Fused Filament Fabrication (FFF)

The present study introduces an approach to additively manufacture non-oxidic Ceramic Matrix Composites (CMCs) by the Material Extrusion (MEX)-based Fused Filament Fabrication. Therefore, highly SiC particle filled thermoplastic filaments were developed containing short fibers and/or long fibers to maintain shape during the thermal treatment and exhibiting flaw tolerant behavior. Polymer Infiltration and Pyrolysis (PIP) was applied to densify the microstructure. It is shown that a low content of long fibers of about 5 % can already exhibit damage tolerance comparable to steel reinforced concrete. Thus, the mechanical behavior is different to conventional fiber composites with significant higher fiber volume content. Nevertheless, these results enable new opportunities for producing advanced complex CMC components by means of Additive Manufacturing (AM).