Journal Jan 2022

Effect of different sources and crushing types on the properties of recycled aggregate concrete Bhashya V., Bharatkumar B. H.

The recycling of waste concrete is beneficial and necessary for the environmental preservation and effective utilization of natural resources. The use of recycled coarse aggregates obtained from construction and demolition waste in new concrete is a solution for effective utilization of construction and demolition waste. In this study, natural aggregates were replaced 100% with recycled aggregates obtained from demolished concrete. Experimental investigations have been carried out on concrete prepared using recycled coarse aggregates obtained from three different sources (Laboratory waste, building of age 10 years and 30 years) and by using two types of jaw crushers, one with flat jaws and other having jaws like V-grooves. Results showed that crushing type of concrete for manufacturing recycled aggregate have a marginal effect on concrete properties. However, there is no significant variation observed in the properties of concrete made with recycled aggregate prepared from different sources (Laboratory waste, building of age 10 years and 30 years).

Analysis of the geometrical properties of fine recycled aggregates using digital image processing technique Jentel De Vlieger, Jiabin Li

The acquisition of natural sand and dumping of fine recycled aggregates (FRA) are two serious environmental problems that can be solved simultaneously by using FRA as replacement of natural sand in high-end applications. In the past, FRA has been considered an unwanted by-product of construction and demolition waste (CDW) processing, due to the high levels of contaminations and high content of fines. However, FRA is currently considered as a new secondary raw material with large potential. Due to the increasing interests in FRA it is of utmost importance to extensively examine their characteristics. To date, research has been done on the water absorption, density, chemical and mineralogical composition, and size distribution of the FRA. However, knowledge on the geometrical properties of FRA is limited. In this paper the geometrical properties of several types of FRA are examined using digital image processing (DIP). The effect of processing methods, crusher openings and crushing cycles are considered to gain new insights into the characteristics of FRA.

Experimental investigation on fresh and hardened properties of geopolymer concrete blended with recycled concrete aggregate Balamurali Kanagaraj, Anand N., Tattukolla Kiran, Prince Arulraj, Justin S.

Geopolymer concrete (GPC) is a sustainable construction material developed from industrial waste products which eliminates the use of cement. Recycling the concrete waste for the development of GPC can satisfy the goals of this sustainable development. Appropriate trials were performed to accomplish a perfect blend of the binder, alkali activator (AA), alkaline liquid to binder ratio and aggregates to develop the GPC. Three types of curing methods namely ambient, sunlight and oven were used for the development of the GPC mixes. This investigation focuses on the assessment of mechanical properties and the microstructure characterization of GPC developed with Natural and Recycled Concrete Aggregates. Fly ash-ground granulated blast furnace slag (FA-GGBS) based recycled concrete aggregate (RCA) blended GPC achieves similar strength to that of GPC blended with Natural coarse aggregate (CA) but with marginal differences. Among all the types of curing, heat cured specimens show higher strength. It is observed that temperature influences the development of early strength gain of GPC with both Natural and Recycled Concrete Aggregate. Increase in AA ratio decreases the workability and increases the strength of GPC mixes. GPC specimens with AA ratio of 1:5 that were cured under ambient condition exhibited minimal strength while GPC mixes with AA ratio of 2.5, showed maximum strength under oven curing condition.

Deflection control of one-way reinforced recycled aggregate concrete members Nikola Tosic, Albert De La Fuente, Snezana Marinkovic

A parametric analysis of deflection control of reinforced recycled aggregate concrete (RAC) one-way members is presented in this study. Within the study, member boundary conditions, ambient conditions (relative humidity), reinforcement ratios, and quasi-permanent–to–design load ratios (as per the Eurocode framework) are varied. Through the analysis, the change in deflections is observed relative to the substitution ratio of RCA (from natural aggregate concrete, NAC, to RAC with 100% of coarse RCA) and span-to-effective depth ratio (L/d). The results of the analysis enable a clear overview of the variability of the deflections of RAC members relative to NAC.

Recycled concrete aggregates in new concrete – full scale demonstration in Navi Mumbai Christian J. Engelsen, Kshemendra Nath P., Sivakumar Kandasami

A full-scale pilot project has been conducted to demonstrate the use of fine recycled concrete aggregates (RCA) for two different concrete qualities with high replacement of natural aggregates. The fine RCA replaced the crushed stone sand fraction in the grade slab (M20) and in the lean concrete (M10) at replacement levels of 50% and 100%, respectively. The RCA concrete was used in the newly constructed precast concrete factory for the affordable housing project of the City and Industrial Development Corporation of Maharashtra Limited (CIDCO).

Concrete rubble was recycled into RCA 0/2 mm by a wet recycling process. The aggregate properties complied with IS: 383 (2016) and the grading achieved was Zone II. The obtained fresh and hardened concrete properties were fully comparable with the reference concrete. The site engineers expressed satisfaction on their experience of using RCA as replacement for CSS, as no placement and finishability issues were encountered. The pilot project has created a desire to continue exploring future opportunities for the use of RCA in concrete.

The price of the fine RCA was competitive even with significant longer transport distance to the construction site than for the CSS aggregates. Hence, there is a potential for significant cost savings in the Mumbai region.

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