Study on the Microstructure of the New Paste of Recycled Aggregate Self-Compacting Concrete

Abstract

Previous literature indicates a decrease in the mechanical properties of various concrete types that contain recycled aggregates (RA), due to their porosity and to their interface of transition zone (ITZ). However, other components of the RA concrete microstructure have not yet been explored, such as the modification of the new paste (NP) with respect to a reference concrete. This paper deals with the microstructure of the new paste of self-compacting concrete (SCC) for different levels of RA. The water to binder ratio (w/b) was kept constant for all concrete mixtures, and equal to 0.5. The SCC mixtures were prepared with percentages of coarse RA of 0%, 30%, 50% and 100%. Mercury intrusion porosimetry test (MIP) and scanning electron microscope (SEM) observations were conducted on the new paste of each concrete. The results indicated that the porosity of the new paste presents a significant variation for replacement percentages of 50% and 100% with respect to NP0 and NP30. However, RA contributed to the refinement of the pore structure of the new paste. The amount of macrospores the diameter of which is in the 50–10,000 nm range was reduced to 20% for NP50 and NP100, while it was about 30% for NP0 and NP30, attributed to the water released by RA. Compressive strength loss for SCC50 and SCC100 concretes are both influenced by porosity of RA, and by the NP porosity. The latter is similar for these two concretes with the 26% increase compared to a reference concrete.

Study of Mechanical Properties of an Eco-Friendly Concrete Containing Recycled Carbon Fiber Reinforced Polymer and Recycled Aggregate

“…The results show that when the RA replacement rate was 30%, the flexural strength decreased by 12.8% compared to that without RA. This is mainly because the bonding of the mortar–NA interface was better than that of the mortar–RA interface, and the tensile strength of RA was lower [ 45 , 46 ].…”

Recycled Coarse Aggregate for Sustainable Self-Compacting Concrete and Mortar

“…Te amount and quality of adhered mortar afect the properties of RCA. Zitouni et al [28] investigated the microstructure of new paste with diferent levels of recycled aggregate in comparison to the normal SCC. 30% RA replacement did not afect the new paste of SCC.…”

Specific Features of the Formation of the Microstructure of Granular Aggregates on Different Binding Compositions (Part 2)

“…2, б. Микроструктура характеризируется как смешанная, состоящая из отдельных блоков-агрегатов и скелетной структуры кристаллических образований гидросиликатов кальция. Смешанная структура имеет различную морфологию [14][15][16][17]. На микроснимке (рис.…”

“…Разные участки поверхности скола ГЗ с шифром 0,315+10 % ВК-2 имеют разную морфо-логию: на одних участках структура представлена параллельно сросшимися кристаллическими пакетами волокон гидросиликатов кальция [11,12], на других разноориентированными призматическим кристаллами эттрингита или гидроксида кальция, на третьих небольшим количеством гексагональных пластинчатых кристаллов алюмосодержащих минералов. Необходимо отметить, что четко просматриваются субмикрокристаллические формирования в виде бахромы [16], наблюдается ряд отдельных мелких блоковагрегатов кристаллической фазы, вероятнее всего образованных путем обрастания частиц наполнителя вяжущей композицией. Структура контактного слоя ГЗ с шифром 0,63+10 % ВК-2 (рис.…”