Tasks
Task 1
This task included all the actions related to the management of the project - strategies for the development of the work plan, the timeline and the duration of the different tasks were defined. During this task, different companies were contacted to establish the partnerships needed to develop the research project.
The greatest obstacle of this task was the establishment of partnerships with agents of the construction sector. These partnerships guaranteed materials and equipment that were indispensable to the development of the different tasks of the project. After various contacts and meetings, agreements were closed with Tecnovia - Sociedade Empreitadas S.A., Soplacas S.A., and Pavicentro - Pré-Fabricação S.A. The facilities used during the two-stage concrete crushing, as well as the precast products with target resistances of 20, 45 and 65 MPa were guaranteed.
Task 2
In task 2 the crushing process was optimized. The feasibility of producing concrete with RA coming from different sources with a pre-determined mechanical strength was also evaluated. In this task precast elements and concrete produced in laboratory conditions, both with compressive strengths of 20, 45 nand65 (± 5) MPa, were crushed to produce RA. The concrete produced in laboratory conditions was made at Instituto Superior Técnico by the research team involved in this project. In total, 7 m3 of concrete were produced. Two crushing processes were tested for each source concrete and resistance: one with a primary crusher – the crusher used was IST’s jaw crusher; and a two-step primary/secondary crushing process, done in the Tecnovia’s Rio Maior quarry. The natural aggregates were also subjected to both crushing processes.
After obtaining the natural and recycled aggregates, a characterization process was conducted, consisting in: grading analysis, density, bulk density, void content, shape index and resistance to fragmentation. The FRA studied were obtained solely by crushing the concrete elements having a compressive strength over 65 MPa. All the sources of concrete were used to test CRA. After crushing, the aggregates were sieved by mechanical processes. The sieving required a considerable effort and time but allowed the production and analysis of recycled aggregates concrete with exactly the same grading curves.
After sieving, three families of concrete were produced, corresponding to the three target-resistances. Each family had six different concrete mixes: two with 100% natural coarse aggregates (one with natural aggregates produced by primary crushing and the other with natural aggregates produced with the stwo-step crushing process); two with 100 % CRA from laboratory-produced concrete (one with CRA produced by primary crushing and the other with CRA produced with the stwo-step crushing process) and two other mixes with CRA generated from precast elements instead of concrete produced in laboratory conditions. The volume of the 18 different concrete mixes produced during this stage was of 2.5 m3.
The concrete mixes were extensively tested, on fresh and hardened states: density, compressive strength in cubes and cylinders, splitting tensile strength, Young’s modulus, abrasion resistance, carbonation resistance, resistance to chloride penetration, water absorption by capillarity and by immersion.
Task 3
Task 3 studied the effects of the resistances of the different sources of RA on the properties of concrete mixes with different incorporation ratios. The results of task 2 and recent investigations led to the decision of not reproducing the compressive strengths of 20 and 45 MPa since these concretes are inadequate to HPC, thus their study is not relevant for the remaining tasks of the project.
Two distinct mixes were produced: PF 65 and LC 65. Both mixes had a target compressive strength of 65 MPa; PF 65 was produced with RA sourced from precast concrete elements whilst LC 65 was produced with RA coming from laboratory-produced concrete elements. The RA incorporation ratios studied were of (FRA / CRA %): 25/25, 50/50; 100/0, 0/100 and 100/100%. 1.8 m3 of concrete were produced.
The rheological, mechanical and durability tests performed in this task were the same as the tests conducted in task 2. Additionally, ultrasonic pulse velocity tests and creep tests were also executed.
Task 4
Task 4’s first objective was the execution of a state-of-the-art concerning tasks 4 and 5: SCC with RA.
The experimental programme of this task was the production of SCC using RA obtained by crushing precast elements with compressive strengths of 45 and 65 MPa. Mixes PF 45 (obtained by crushing SC with compressive resistance of 45 MPa) and PF 65 (obtained by crushing SC with compressive resistance of 45 MPa) were studied.
The experimental campaign of task 4 started with the production of self-compacting mortars. Preliminary tests on mortars were conducted in order to determine the proportions of the SCC mixes: the w/c ratio and superplasticizer quantities were adjusted before coarse aggregate (either recycled or coarse) incorporation, allowing a preliminary evaluation of workability. Four mortars were studied and originated five concretes for each strength class (FRA / CRA (%)): 0/0; 25/25; 50/50; 0/100; 100/0.
The fresh state SCC was tested with the intent of evaluating its self-compacting properties: flow, flow rate, viscosity, filling capacity, confined flow, segregation resistance, passing ability and blocking resistance tests were made. The concrete specimens were subjected to the following tests: density, compressive strength in cubes, compressive strength in cylinders, splitting tensile strength, Young’s modulus, ultrasonic pulse velocity, abrasion resistance, creep deformation, shrinkage deformation, oxygen permeability, water absorption by immersion, water absorption by capillarity, chloride penetration resistance, electric resistivity and carbonation resistance. From these tests a detrimental effect of RA incorporation on these properties was observed in both concrete families. 1.5 m3 of concrete were produced in this stage.
Task 5
Task 5 studied the incorporation of RA produced from precast elements on HPC, self-compacting or not. The results of the previous tasks were thoroughly analysed and it was concluded that the RA generated from the precast elements of the highest strength class could have the required potential for HPC production. An attempt to improve the characteristics of recycled aggregates HPC was made, with a focus on target resistances above 90 MPa. Different parameters were optimized: cement ratio and cement type, superplasticizer ratio, silica fume ratio and fly ash ratio.
Natural aggregates HPC were studied in three experimental stages. The two first stages had different assumptions: in the first stage silica fume and fly ash were used as cement replacements with a fixed binder quantity of 400 kg/m3. On the second stage, cement content was fixed at 550 kg/m3. Fly ash and silica fume were introduced as complementary products in this stage. In the first stage the aggregates had a maximum particle size of 22.4 mm, whilst in the second stage the aggregates had a maximum particle size of 16 mm. The mixing process was also changed between stages: in the first stage a difficulty in silica fume dispersion was witnessed and agglomerations of this material were a possibility; on the second stage a new concrete mixer, with vertical axis, was used and a different batch process was considered. On both stages, three ratios of silica fume were studied (0, 5 and 10%) as well as three FRA / CRA incorporation ratios (50/50; 0/100 and 100/100%). The following tests were analysed: compressive strength, splitting tensile strength, Young’s modulus, ultrasonic pulse velocity, carbonation resistance, chloride penetration resistance, water absorption by capillarity and water absorption by immersion.
Finally, the third stage of the conventional HPC experimental programme consisted in choosing six concrete mixes of the previous stages in order to conduct additional testing. These tests were the following: scanning electron microscopy, shrinkage, creep, oxygen permeability and steel / concrete bond. The choise of the mixes considered the effect of RA and silica fume on HPC performance. The three phases required the production of 3 m3 of concrete.
A preliminary study regarding self-compacting mortars and concretes with the intent to determine the quantity of cement and silica fume in the production of high-strength self-compacting concrete was conducted.
Once the quantities of cement and silica fume were determined, all the mixing parameters were fixed and the only substitutions made were at the natural aggregate level. Four self-compacting mortar mixes were produced: one only with natural fine aggregates, whilst the others had different FRA incorporation ratios (25, 50 and 100%). Six different concretes were generated with the four mortar mixes studied. The different FRA/CRA incorporation ratios were as follows (%): 0/0; 25/25; 50/50; 100/100; 0/100; 100/0. Approximately 1 m3 of concrete was produced in this task.
As in Task 4, the fresh concrete properties of the SCC was evaluated by five different tests. As planned, the concrete specimens were subject of the same tests as the SCC of Task 4, except the 182 day durability tests. A trend of decreasing durability performance due to RA incorporation was witnessed.
Task 6
Task 6 aimed at developing rules towards the incorporation of FRA and CRA produced from precast elements on HPC concrete. A technical specification that complements the specification LNEC E 471 was proposed. The latter specification is only related to the conditions of RCA use on concretes with hydraulic binders.
This specification proposal was based on the results of the experiments made during the experimental campaign, including the aggregate testing and the tests made on the HPC produced.
The work developed in this project showed the feasibility of incorporating RA on HPC concrete, although a variable maximum incorporation ratio had to be established for different concrete uses in order to comply with their respective requirements. The proposed specification defines classification classes of RA dependent on the target performance (compressive strength at 28 days, Young’s modulus at 28 days, splitting tensile strength at 28 days, water absorption at 28 days, water absorption by capillarity, carbonation resistance at 28 days and resistance to chloride penetration at 91 days) achieved.
This task included all the actions related to the management of the project - strategies for the development of the work plan, the timeline and the duration of the different tasks were defined. During this task, different companies were contacted to establish the partnerships needed to develop the research project.
The greatest obstacle of this task was the establishment of partnerships with agents of the construction sector. These partnerships guaranteed materials and equipment that were indispensable to the development of the different tasks of the project. After various contacts and meetings, agreements were closed with Tecnovia - Sociedade Empreitadas S.A., Soplacas S.A., and Pavicentro - Pré-Fabricação S.A. The facilities used during the two-stage concrete crushing, as well as the precast products with target resistances of 20, 45 and 65 MPa were guaranteed.
Task 2
In task 2 the crushing process was optimized. The feasibility of producing concrete with RA coming from different sources with a pre-determined mechanical strength was also evaluated. In this task precast elements and concrete produced in laboratory conditions, both with compressive strengths of 20, 45 nand65 (± 5) MPa, were crushed to produce RA. The concrete produced in laboratory conditions was made at Instituto Superior Técnico by the research team involved in this project. In total, 7 m3 of concrete were produced. Two crushing processes were tested for each source concrete and resistance: one with a primary crusher – the crusher used was IST’s jaw crusher; and a two-step primary/secondary crushing process, done in the Tecnovia’s Rio Maior quarry. The natural aggregates were also subjected to both crushing processes.
After obtaining the natural and recycled aggregates, a characterization process was conducted, consisting in: grading analysis, density, bulk density, void content, shape index and resistance to fragmentation. The FRA studied were obtained solely by crushing the concrete elements having a compressive strength over 65 MPa. All the sources of concrete were used to test CRA. After crushing, the aggregates were sieved by mechanical processes. The sieving required a considerable effort and time but allowed the production and analysis of recycled aggregates concrete with exactly the same grading curves.
After sieving, three families of concrete were produced, corresponding to the three target-resistances. Each family had six different concrete mixes: two with 100% natural coarse aggregates (one with natural aggregates produced by primary crushing and the other with natural aggregates produced with the stwo-step crushing process); two with 100 % CRA from laboratory-produced concrete (one with CRA produced by primary crushing and the other with CRA produced with the stwo-step crushing process) and two other mixes with CRA generated from precast elements instead of concrete produced in laboratory conditions. The volume of the 18 different concrete mixes produced during this stage was of 2.5 m3.
The concrete mixes were extensively tested, on fresh and hardened states: density, compressive strength in cubes and cylinders, splitting tensile strength, Young’s modulus, abrasion resistance, carbonation resistance, resistance to chloride penetration, water absorption by capillarity and by immersion.
Task 3
Task 3 studied the effects of the resistances of the different sources of RA on the properties of concrete mixes with different incorporation ratios. The results of task 2 and recent investigations led to the decision of not reproducing the compressive strengths of 20 and 45 MPa since these concretes are inadequate to HPC, thus their study is not relevant for the remaining tasks of the project.
Two distinct mixes were produced: PF 65 and LC 65. Both mixes had a target compressive strength of 65 MPa; PF 65 was produced with RA sourced from precast concrete elements whilst LC 65 was produced with RA coming from laboratory-produced concrete elements. The RA incorporation ratios studied were of (FRA / CRA %): 25/25, 50/50; 100/0, 0/100 and 100/100%. 1.8 m3 of concrete were produced.
The rheological, mechanical and durability tests performed in this task were the same as the tests conducted in task 2. Additionally, ultrasonic pulse velocity tests and creep tests were also executed.
Task 4
Task 4’s first objective was the execution of a state-of-the-art concerning tasks 4 and 5: SCC with RA.
The experimental programme of this task was the production of SCC using RA obtained by crushing precast elements with compressive strengths of 45 and 65 MPa. Mixes PF 45 (obtained by crushing SC with compressive resistance of 45 MPa) and PF 65 (obtained by crushing SC with compressive resistance of 45 MPa) were studied.
The experimental campaign of task 4 started with the production of self-compacting mortars. Preliminary tests on mortars were conducted in order to determine the proportions of the SCC mixes: the w/c ratio and superplasticizer quantities were adjusted before coarse aggregate (either recycled or coarse) incorporation, allowing a preliminary evaluation of workability. Four mortars were studied and originated five concretes for each strength class (FRA / CRA (%)): 0/0; 25/25; 50/50; 0/100; 100/0.
The fresh state SCC was tested with the intent of evaluating its self-compacting properties: flow, flow rate, viscosity, filling capacity, confined flow, segregation resistance, passing ability and blocking resistance tests were made. The concrete specimens were subjected to the following tests: density, compressive strength in cubes, compressive strength in cylinders, splitting tensile strength, Young’s modulus, ultrasonic pulse velocity, abrasion resistance, creep deformation, shrinkage deformation, oxygen permeability, water absorption by immersion, water absorption by capillarity, chloride penetration resistance, electric resistivity and carbonation resistance. From these tests a detrimental effect of RA incorporation on these properties was observed in both concrete families. 1.5 m3 of concrete were produced in this stage.
Task 5
Task 5 studied the incorporation of RA produced from precast elements on HPC, self-compacting or not. The results of the previous tasks were thoroughly analysed and it was concluded that the RA generated from the precast elements of the highest strength class could have the required potential for HPC production. An attempt to improve the characteristics of recycled aggregates HPC was made, with a focus on target resistances above 90 MPa. Different parameters were optimized: cement ratio and cement type, superplasticizer ratio, silica fume ratio and fly ash ratio.
Natural aggregates HPC were studied in three experimental stages. The two first stages had different assumptions: in the first stage silica fume and fly ash were used as cement replacements with a fixed binder quantity of 400 kg/m3. On the second stage, cement content was fixed at 550 kg/m3. Fly ash and silica fume were introduced as complementary products in this stage. In the first stage the aggregates had a maximum particle size of 22.4 mm, whilst in the second stage the aggregates had a maximum particle size of 16 mm. The mixing process was also changed between stages: in the first stage a difficulty in silica fume dispersion was witnessed and agglomerations of this material were a possibility; on the second stage a new concrete mixer, with vertical axis, was used and a different batch process was considered. On both stages, three ratios of silica fume were studied (0, 5 and 10%) as well as three FRA / CRA incorporation ratios (50/50; 0/100 and 100/100%). The following tests were analysed: compressive strength, splitting tensile strength, Young’s modulus, ultrasonic pulse velocity, carbonation resistance, chloride penetration resistance, water absorption by capillarity and water absorption by immersion.
Finally, the third stage of the conventional HPC experimental programme consisted in choosing six concrete mixes of the previous stages in order to conduct additional testing. These tests were the following: scanning electron microscopy, shrinkage, creep, oxygen permeability and steel / concrete bond. The choise of the mixes considered the effect of RA and silica fume on HPC performance. The three phases required the production of 3 m3 of concrete.
A preliminary study regarding self-compacting mortars and concretes with the intent to determine the quantity of cement and silica fume in the production of high-strength self-compacting concrete was conducted.
Once the quantities of cement and silica fume were determined, all the mixing parameters were fixed and the only substitutions made were at the natural aggregate level. Four self-compacting mortar mixes were produced: one only with natural fine aggregates, whilst the others had different FRA incorporation ratios (25, 50 and 100%). Six different concretes were generated with the four mortar mixes studied. The different FRA/CRA incorporation ratios were as follows (%): 0/0; 25/25; 50/50; 100/100; 0/100; 100/0. Approximately 1 m3 of concrete was produced in this task.
As in Task 4, the fresh concrete properties of the SCC was evaluated by five different tests. As planned, the concrete specimens were subject of the same tests as the SCC of Task 4, except the 182 day durability tests. A trend of decreasing durability performance due to RA incorporation was witnessed.
Task 6
Task 6 aimed at developing rules towards the incorporation of FRA and CRA produced from precast elements on HPC concrete. A technical specification that complements the specification LNEC E 471 was proposed. The latter specification is only related to the conditions of RCA use on concretes with hydraulic binders.
This specification proposal was based on the results of the experiments made during the experimental campaign, including the aggregate testing and the tests made on the HPC produced.
The work developed in this project showed the feasibility of incorporating RA on HPC concrete, although a variable maximum incorporation ratio had to be established for different concrete uses in order to comply with their respective requirements. The proposed specification defines classification classes of RA dependent on the target performance (compressive strength at 28 days, Young’s modulus at 28 days, splitting tensile strength at 28 days, water absorption at 28 days, water absorption by capillarity, carbonation resistance at 28 days and resistance to chloride penetration at 91 days) achieved.