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Q: ASR - what is the impact and mitigation in concrete structures?
A: Summary
Alkali Silica Reaction or ASR is the reaction between the aggregate and the cement paste in concrete which forms a reaction product that causes the concrete mass to expand. The expansion pressure causes reinforced concrete to crack and non-reinforced to grow. The reaction is between acidic silicate aggregate components and the alkali components of the cement paste such as sodium and potassium oxides.
The first defense against ASR is to evaluate the sources of aggregate for reactive components and avoid using these sources or take preventative action in the mix design. There are several methods for testing aggregate. The most commonly used are ASTM-1567, an accelerated bar expansion test and inspection by petrographic analysis. If the only aggregate available has some ASR potential there are two things that can be done to inhibit the reaction. Fly ash can be added to the mix at the rate of 25% of the cement content. This will form Pozlonic cement having a lower active alkali content as indicated by a drop in pH from 13 to 9. The other option is to add a lithium salt to the mix, such as lithium nitrate, at a 1 to 1 ratio with the measured alkali content of the cement. The lithium reacts with the aggregate acid sites and forms a non expansive gel, thus reducing the sites available for reaction with potassium and sodium elements in the cement.
If an in place concrete begins to show signs of ASR damage in the form of a random crack pattern, remedial action can be taken to inhibit expansion of existing ASR gel and to inhibit further ASR reaction. The application of a silane type water repellent will inhibit moisture from being absorbed by the ASR gel and reduce further expansion and crack propagation.
A lithium salt containing formulation can be applied to the concrete surface and allowed to penetrate and transport lithium ions into the cement where their reaction with the reactive aggregate sites will reduce the potential for further ASR gel formation.
Surtreat Holding, LLC has developed formulations and application methods for all of the prescribed ASR control methods.
ASR DETECTION AND MEASUREMENT
There 11 ASTM methods for evaluating aggregate and methods like fly ash and lithium addition to mitigate ASR. All of these are based on the bar expansion method where a concrete bar is measured for growth in length during an aging period as a means of determining the degree of ASR activity. If the bar expansion is less than 0.1% after 100 days then it can be assume that there is no ASR problem, Active aggregate will typically give a growth of 0.5% in 50 days or less depending on the test method used.
REMEDIATION OF ASR DAMAGED CONCRETE
When a concrete structure has established symptoms of ASR a significant amount of expanding gel has been formed. The symptoms are:
General growth of non-reinforced concrete in length and width along with aggregate popping from the surface.
Random crack formation in reinforced concrete where expansion is constrained and relieved by crack formation.
A 40% solution of a silane type water repellent when applied to a concrete test bar and evaluated using ASTM 1293 has kept expansion at 0.06% while a control bar gave 1.2% expansion at the end of a 50 week test period. The silane also kept the wet test cycle weight gain close to zero while the control increased by 15%. The prevention of water adsorption has significantly reduced gel production and expansion and subsequent bar growth. Surtreat Holding has several silane and siloxane water repellent formulations that will penetrate into concrete and prevent water adsorption and reduce ASR damage.
The addition of lithium nitrate to a concrete mix in a ratio of 0.8 moles of lithium per mole of cement sodium content kept concrete bar expansion below 0.1% at the end of a 200 day test period while the control bar expanded by 0.6%. As a general guide the placement of 100PPM of lithium in the concrete cement paste is a target for controlling ASR. It is easy to put any amount of lithium in a concrete mix as an admixture. The difficulty is to put a critical amount in hard concrete that is exhibiting symptoms of ASR. Surtreat has lithium containing formulations that can be applied to the concrete surface and will penetrate and allow lithium to slowly migrate into the whole concrete mass. Surtreat also has a process for injecting the lithium formulation into concrete. This enables a higher initial loading and deeper initial penetration. For example, a project was performed on a New Jersey Turnpike bridge piers and beams that were exhibiting an ASR crack pattern. A lithium formulation was injected into all sides of the piers and beams at a target concentration of 300PPM in the cement paste at 6 inches. Core samples were taken 6 months after and analyzed for lithium and corrected for baseline lithium concentration. Most of the lithium was in the first 2 inches, but the lithium concentration in the cement paste was above the baseline concentration at 4 and 6 inches indicating that lithium was slowly migrating into the whole mass. The average lithium concentration in the cement paste was 210 PPM significantly above the 100PPM minimum target concentration for controlling ASR. After injection of the lithium, the concrete surface was covered with Surcoat to seal the ASR expansion cracks and then a water repellent was applied. To the extent reported no further ASR cracking has been observed.
SURTREAT HOLDING, LLC RECOMMENDED PROCESS FOR PREVENTION AND CONTROL OF ASR
NEW CONCRETE POUR
For new concrete pours where aggregate with suspected ASR potential is used, Surtreat recommends that a lithium compound be added to the mix at the rate of 1 part of lithium per part of sodium and potassium content in the cement.
EXISTING CONCRETE STRUCTURES EXHIBITING ASR SYMPTOMS
A quantity of a lithium containing formulation be applied to the concrete surface and penetrated into the cement in an amount that will equal 100PPM of lithium concentration in the cement paste of the whole concrete mass. This can be done by applying a formulation designed to penetrate the surface or by a surface injection method. A coat of a latex modified cement coating such as Surtreat Surcoat is applied to the surface to cover and seal the ASR cracks. When the Surcoat is cured two application of a silane or siloxane or mixture of both is applied to the surface at the rate of 100ft2gal.
Robert A. Walde, Chief Technical Officer, Surtreat Holding, LLC contact
Q: ASR - what is the impact and mitigation in concrete structures?
A: Summary
Alkali Silica Reaction or ASR is the reaction between the aggregate and the cement paste in concrete which forms a reaction product that causes the concrete mass to expand. The expansion pressure causes reinforced concrete to crack and non-reinforced to grow. The reaction is between acidic silicate aggregate components and the alkali components of the cement paste such as sodium and potassium oxides.
The first defense against ASR is to evaluate the sources of aggregate for reactive components and avoid using these sources or take preventative action in the mix design. There are several methods for testing aggregate. The most commonly used are ASTM-1567, an accelerated bar expansion test and inspection by petrographic analysis. If the only aggregate available has some ASR potential there are two things that can be done to inhibit the reaction. Fly ash can be added to the mix at the rate of 25% of the cement content. This will form Pozlonic cement having a lower active alkali content as indicated by a drop in pH from 13 to 9. The other option is to add a lithium salt to the mix, such as lithium nitrate, at a 1 to 1 ratio with the measured alkali content of the cement. The lithium reacts with the aggregate acid sites and forms a non expansive gel, thus reducing the sites available for reaction with potassium and sodium elements in the cement.
If an in place concrete begins to show signs of ASR damage in the form of a random crack pattern, remedial action can be taken to inhibit expansion of existing ASR gel and to inhibit further ASR reaction. The application of a silane type water repellent will inhibit moisture from being absorbed by the ASR gel and reduce further expansion and crack propagation.
A lithium salt containing formulation can be applied to the concrete surface and allowed to penetrate and transport lithium ions into the cement where their reaction with the reactive aggregate sites will reduce the potential for further ASR gel formation.
Surtreat Holding, LLC has developed formulations and application methods for all of the prescribed ASR control methods.
ASR DETECTION AND MEASUREMENT
There 11 ASTM methods for evaluating aggregate and methods like fly ash and lithium addition to mitigate ASR. All of these are based on the bar expansion method where a concrete bar is measured for growth in length during an aging period as a means of determining the degree of ASR activity. If the bar expansion is less than 0.1% after 100 days then it can be assume that there is no ASR problem, Active aggregate will typically give a growth of 0.5% in 50 days or less depending on the test method used.
REMEDIATION OF ASR DAMAGED CONCRETE
When a concrete structure has established symptoms of ASR a significant amount of expanding gel has been formed. The symptoms are:
General growth of non-reinforced concrete in length and width along with aggregate popping from the surface.
Random crack formation in reinforced concrete where expansion is constrained and relieved by crack formation.
A 40% solution of a silane type water repellent when applied to a concrete test bar and evaluated using ASTM 1293 has kept expansion at 0.06% while a control bar gave 1.2% expansion at the end of a 50 week test period. The silane also kept the wet test cycle weight gain close to zero while the control increased by 15%. The prevention of water adsorption has significantly reduced gel production and expansion and subsequent bar growth. Surtreat Holding has several silane and siloxane water repellent formulations that will penetrate into concrete and prevent water adsorption and reduce ASR damage.
The addition of lithium nitrate to a concrete mix in a ratio of 0.8 moles of lithium per mole of cement sodium content kept concrete bar expansion below 0.1% at the end of a 200 day test period while the control bar expanded by 0.6%. As a general guide the placement of 100PPM of lithium in the concrete cement paste is a target for controlling ASR. It is easy to put any amount of lithium in a concrete mix as an admixture. The difficulty is to put a critical amount in hard concrete that is exhibiting symptoms of ASR. Surtreat has lithium containing formulations that can be applied to the concrete surface and will penetrate and allow lithium to slowly migrate into the whole concrete mass. Surtreat also has a process for injecting the lithium formulation into concrete. This enables a higher initial loading and deeper initial penetration. For example, a project was performed on a New Jersey Turnpike bridge piers and beams that were exhibiting an ASR crack pattern. A lithium formulation was injected into all sides of the piers and beams at a target concentration of 300PPM in the cement paste at 6 inches. Core samples were taken 6 months after and analyzed for lithium and corrected for baseline lithium concentration. Most of the lithium was in the first 2 inches, but the lithium concentration in the cement paste was above the baseline concentration at 4 and 6 inches indicating that lithium was slowly migrating into the whole mass. The average lithium concentration in the cement paste was 210 PPM significantly above the 100PPM minimum target concentration for controlling ASR. After injection of the lithium, the concrete surface was covered with Surcoat to seal the ASR expansion cracks and then a water repellent was applied. To the extent reported no further ASR cracking has been observed.
SURTREAT HOLDING, LLC RECOMMENDED PROCESS FOR PREVENTION AND CONTROL OF ASR
NEW CONCRETE POUR
For new concrete pours where aggregate with suspected ASR potential is used, Surtreat recommends that a lithium compound be added to the mix at the rate of 1 part of lithium per part of sodium and potassium content in the cement.
EXISTING CONCRETE STRUCTURES EXHIBITING ASR SYMPTOMS
A quantity of a lithium containing formulation be applied to the concrete surface and penetrated into the cement in an amount that will equal 100PPM of lithium concentration in the cement paste of the whole concrete mass. This can be done by applying a formulation designed to penetrate the surface or by a surface injection method. A coat of a latex modified cement coating such as Surtreat Surcoat is applied to the surface to cover and seal the ASR cracks. When the Surcoat is cured two application of a silane or siloxane or mixture of both is applied to the surface at the rate of 100ft2gal.
Robert A. Walde, Chief Technical Officer, Surtreat Holding, LLC contact
Surtreat Holding, LLC 437 Grant Street, Pittsburgh, PA 15219; 412.281.1202, official website www.surtreat.info
Max Merzlikin, Surtreat Holding, LLC 2015