scholarly journals The use of lithium salts and supplementary cementing materials to control reactivity of recycled concrete aggregate

2021 ◽  
Author(s):  
Waleed Mikhaiel
Keyword(s):  
Preventive Measure ◽  
Calcium Content ◽  
Recycled Concrete ◽  
Alkali Silica Reaction ◽  
Alkaline Solutions ◽  
Concrete Aggregate ◽  
Second Phase ◽  
Lithium Nitrate ◽  
Recycled Concrete Aggregate ◽  
Supplementary Cementing Materials

This thesis covered the second phase of a study that focused on the reactivity of recycled concrete aggregate (RCA) produced from concrete affected by alkali-silica reaction (ASR). The first phase investigated the reactivity of ASR-affected RCA and the use of Supplementary Cementing Materials (SCM) as a preventive measure. The second phase was carried out to study the efficacy of lithium nitrate, when used individually and in combination with SCM, in suppressing the reactivity of RCA. The use of different dosages of lithium nitrate combined with SCMs reduced expansion due to ASR. However, the expansion results showed that increasing the dosage of lithium beyond a certain level does not help in suppressing the expansion. The high reacitivity of the tested RCA was attiributable to its relatively high alkalis and calcium hydroxide contents that fuel further ASR. The alkalis consumed or contributed from RCA were evaluated through leaching the aggregate particles in distilled water and alkaline solutions at different molarities with and without lithium nitrate. Alkalis consumption was found to decrease when lithium was presented in the leaching solutions. Examining RCA samples under scanning electron microscope (SEM) showed that the crushing process of the RCA exposes fresh surfaces of the reactive virgin aggregate and creates cracks within the particles that provide an easy path of alkalis to reactive sites within the RCA. Examination of the composition of ASR gel showed that exposing the RCA to lithium solution decreased the calcium content and Ca/Si of the gel. This could add to the suggested mechanisms by which the lithium mitigates ASR.

scholarly journals The use of lithium salts and supplementary cementing materials to control reactivity of recycled concrete aggregate

2021 ◽  
Author(s):  
Waleed Mikhaiel
Keyword(s):  
Preventive Measure ◽  
Calcium Content ◽  
Recycled Concrete ◽  
Alkali Silica Reaction ◽  
Alkaline Solutions ◽  
Concrete Aggregate ◽  
Second Phase ◽  
Lithium Nitrate ◽  
Recycled Concrete Aggregate ◽  
Supplementary Cementing Materials

This thesis covered the second phase of a study that focused on the reactivity of recycled concrete aggregate (RCA) produced from concrete affected by alkali-silica reaction (ASR). The first phase investigated the reactivity of ASR-affected RCA and the use of Supplementary Cementing Materials (SCM) as a preventive measure. The second phase was carried out to study the efficacy of lithium nitrate, when used individually and in combination with SCM, in suppressing the reactivity of RCA. The use of different dosages of lithium nitrate combined with SCMs reduced expansion due to ASR. However, the expansion results showed that increasing the dosage of lithium beyond a certain level does not help in suppressing the expansion. The high reacitivity of the tested RCA was attiributable to its relatively high alkalis and calcium hydroxide contents that fuel further ASR. The alkalis consumed or contributed from RCA were evaluated through leaching the aggregate particles in distilled water and alkaline solutions at different molarities with and without lithium nitrate. Alkalis consumption was found to decrease when lithium was presented in the leaching solutions. Examining RCA samples under scanning electron microscope (SEM) showed that the crushing process of the RCA exposes fresh surfaces of the reactive virgin aggregate and creates cracks within the particles that provide an easy path of alkalis to reactive sites within the RCA. Examination of the composition of ASR gel showed that exposing the RCA to lithium solution decreased the calcium content and Ca/Si of the gel. This could add to the suggested mechanisms by which the lithium mitigates ASR.

scholarly journals Testing recycled concrete aggregate suffering different levels of alkali-silica reaction for use in new structures

2021 ◽  
Author(s):  
Matthew Piersanti
Keyword(s):  
Service Life ◽  
Recycled Concrete ◽  
Alkali Silica Reaction ◽  
Concrete Aggregate ◽  
Recycled Concrete Aggregate ◽  
Construction Work ◽  
Supplementary Cementing Materials ◽  
New Construction ◽  
Land Space ◽  
Different Levels

As concrete reaches the end of its service life, it is demolished and placed in landfills, which is not sustainable as this consumes land space. Many demolished structures are crushed into recycled concrete aggregate (RCA) and used in new construction work to reduce concrete waste. To be used in concrete, the effects of RCA on the new structures should be carefully examined. The RCA studied in this research is an alkali-silica reactive gravel from Sudbury, Ontario. The RCA was obtained from different elements of a 20-year old bridge that suffered different levels of deterioration. It was determined that the level of deterioration that affected the previous structure does not significantly affect the expansion that will occur in the new structure. It was also determined that the expansion could be mitigated through the use of supplementary cementing materials although higher levels are required compared those required for the virgin aggregate.

scholarly journals Testing recycled concrete aggregate suffering different levels of alkali-silica reaction for use in new structures

2021 ◽  
Author(s):  
Matthew Piersanti
Keyword(s):  
Service Life ◽  
Recycled Concrete ◽  
Alkali Silica Reaction ◽  
Concrete Aggregate ◽  
Recycled Concrete Aggregate ◽  
Construction Work ◽  
Supplementary Cementing Materials ◽  
New Construction ◽  
Land Space ◽  
Different Levels

As concrete reaches the end of its service life, it is demolished and placed in landfills, which is not sustainable as this consumes land space. Many demolished structures are crushed into recycled concrete aggregate (RCA) and used in new construction work to reduce concrete waste. To be used in concrete, the effects of RCA on the new structures should be carefully examined. The RCA studied in this research is an alkali-silica reactive gravel from Sudbury, Ontario. The RCA was obtained from different elements of a 20-year old bridge that suffered different levels of deterioration. It was determined that the level of deterioration that affected the previous structure does not significantly affect the expansion that will occur in the new structure. It was also determined that the expansion could be mitigated through the use of supplementary cementing materials although higher levels are required compared those required for the virgin aggregate.

Microscopic assessment of recycled concrete aggregate (RCA) mixtures affected by alkali-silica reaction (ASR)

2021 ◽  
Vol 269 ◽  
pp. 121250
Author(s):  
Cassandra Trottier ◽  
Andisheh Zahedi ◽  
Rouzbeh Ziapour ◽  
Leandro Sanchez ◽  
Francisco Locati
Keyword(s):  
Recycled Concrete ◽  
Alkali Silica Reaction ◽  
Concrete Aggregate ◽  
Recycled Concrete Aggregate

scholarly journals Studies on the fresh properties an durability of unshrinkable fill containing recycled concrete aggregate or natural aggregates of marginal quality

2021 ◽  
Author(s):  
Maryam Kolahdoozan
Keyword(s):  
Calcium Content ◽  
Recycled Concrete ◽  
Expansion Rate ◽  
Concrete Aggregate ◽  
Recycled Concrete Aggregate ◽  
Sulphate Attack ◽  
Fresh Properties ◽  
Severe Damage ◽  
Sulphate Content ◽  
Natural Aggregates

The intention of this research is to explore the feasibility of incorporating aggregates of low or marginal quality, such as Recycled Concrete Aggregate (RCA) and aggregate with high sulphate content, in U-fill mixtures. It has been determined that where RCA is used, water dissipation may be hindered due to the increase in fines caused by abrasion, hence causing an increase in hardening time. To reduce this effect, addition of natural aggregates may be necessary. Moreover, through a series of investigation it has been found that high percentages of sulphate may cause severe damage due to Ettringite and Thaumasite formation; however by incorporation of supplementary materials such as slag the deleterious effects of internal sulphate attack can be reduced. The effects of using Na2SO4 and gypsum in the presence of slag have also been investigated. Results indicated that due to the lower available calcium content within bars containing Na2SO4 expansion rate is low.

scholarly journals Studies on the fresh properties an durability of unshrinkable fill containing recycled concrete aggregate or natural aggregates of marginal quality

2021 ◽  
Author(s):  
Maryam Kolahdoozan
Keyword(s):  
Calcium Content ◽  
Recycled Concrete ◽  
Expansion Rate ◽  
Concrete Aggregate ◽  
Recycled Concrete Aggregate ◽  
Sulphate Attack ◽  
Fresh Properties ◽  
Severe Damage ◽  
Sulphate Content ◽  
Natural Aggregates

The intention of this research is to explore the feasibility of incorporating aggregates of low or marginal quality, such as Recycled Concrete Aggregate (RCA) and aggregate with high sulphate content, in U-fill mixtures. It has been determined that where RCA is used, water dissipation may be hindered due to the increase in fines caused by abrasion, hence causing an increase in hardening time. To reduce this effect, addition of natural aggregates may be necessary. Moreover, through a series of investigation it has been found that high percentages of sulphate may cause severe damage due to Ettringite and Thaumasite formation; however by incorporation of supplementary materials such as slag the deleterious effects of internal sulphate attack can be reduced. The effects of using Na2SO4 and gypsum in the presence of slag have also been investigated. Results indicated that due to the lower available calcium content within bars containing Na2SO4 expansion rate is low.

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