THE EFFECT OF SILICA FUME AND FLY ASH ON ALKALI-SILICA REACTION (ASR) Kamile TOSUN Halit YAZICI Bülent BARADAN Civil Engineering Department

Transcription

1 THE EFFECT OF SILICA FUME AND FLY ASH ON ALKALI-SILICA REACTION (ASR) Kamile TOSUN Halit YAZICI Bülent BARADAN Civil Engineering Department

2 ALKALI-SILICA REACTION (ASR) in CONCRETE IS an EXPANSIVE CHEMICAL REACTION BETWEEN ALKALIS and REACTIVE FORMS OF SILICA IN CERTAIN AGGREGATES, WHICH MAY CAUSE THE DETERIORATION of CONCRETE.

3 ASR CAN BE EXPLAINED AS A TWO-STEP PROCESS : 1. ALKALI + SILICA ASR GEL 2. ASR GEL + WATER EXPANSION Water and/or alkalis from the environment (e.g. from de-icing salts) DETERIORATION of CONCRETE Diffusion of alkalis (e.g. from cement and admixtures) Diffusion of water and alkalis into concrete Crack formation (map cracking and surface parallel cracking) ASR gel; expansion Reactive Aggregate

4 THREE REQUIREMENTS MUST BE MET FOR THE PROGRESS of EXPANSIVE ASR : 1) REACTIVE FORMS OF SILICA FROM THE AGGREGATE 2) SUFFICIENT ALKALI CONTENT (PRIMARILY FROM THE CEMENT) 3) MOISTURE IN THE CONCRETE

5 SOURCES of ALKALIS CEMENT AGGREGATE MIXING WATER CHEMICAL AND MINERAL ADMIXTURES INDUSTRIAL WASTE WATER DE-ICING SALTS SEA WATER ALKALI MIGRATION (CYCLING WETTING AND DRYING, FREEZING AND THAWING, ELECTRICAL CURRENTS) { (Na 2 O) e = Na 2 O K 2 O } THE CEMENTS with LESS THAN 0.6 % EQUIVALENT Na 2 O are CLASSIFIED LOW ALKALI CEMENT

6 REACTIVITY of an AGGREGATE REACTIVE FORMS OF SILICA OPAL COMPOSITION GEOLOGICAL ORIGIN TEXTURAL CHARACTERISTICS CHALCEDONY CRISTOBALITE TRIDYMITE CRYPTOCRISTALLINE QUARTZ REACTIVE MINERALS OCCUR IN OPALINE or CHALCEDONIC CHERTS SILICEOUS LIMESTONES RYHOLITE and RYHOLITIC TUFFS ANDESITE and ANDESITE TUFFS

7 ASR DAMAGES MAP CRACKING EXPANSION POP-OUTS GEL EXUDATION VARIATION IN COLOUR OF CONCRETE

8 EFFECTIVE MEASURES IN CONTROLLING ASR EXPANSION CONTROLLING the AMOUNT of REACTIVE SILICA LIMITING the ALKALI CONTENT of CONCRETE CONTROLLING the MOISTURE CONTENT of CONCRETE REDUCING the PERMEABILITY of CONCRETE USING MINERAL or CHEMICAL ADMIXTURES (Silica Fume, Fly Ash, Salts Of Lithium etc.) SOME of THESE METHODS MAY BE IMPLEMENTED TOGETHER

9 SILICA FUME and FLY ASH MAY HAVE VERY POSITIVE EFFECTS IN PREVENTING EXPANSION DUE TO ASR REDUCING HYDROXYL CONCENTRATION WHEN USED AS A PARTIAL REPLACEMENT FOR HIGH ALKALI CEMENT WHEN USED AS A PARTIAL REPLACEMENT FOR REACTIVE SAND SILICA FUME PROMOTES ASR while the CONCRETE in FRESH STATE IMPROVED IMPERMEABILITY REDUCING SOLUBILITY of REACTIVE SILICA ALKALI DILUTERS REACTIVE SILICA DILUTERS ALKALIS DEPLETED DUE TO THIS RAPID REACTION PREVENT WATER PENETRATION, and ALKALI MIGRATION

10 EXPERIMENTAL STUDY THE EFFECTIVENESS OF INCORPORATING FLY ASH (CLASS C) AND/OR SILICA FUME IN PREVENTING EXPANSION DUE TO ASR HAS BEEN INVESTIGATED REACTIVE SAND: FROM AHMETLİ REGION NEAR İZMİR CLASS C FLY ASH : FROM SOMA B POWER PLANT SILICA FUME: PRODUCT of YKS/SKW CONSTRUCTION CHEMICALS HIGH ALKALI CEMENT: PC 42,5 (Na 2 O) e = 0.91 % > 0.6 % REACTIVITY of CEMENT- AGGREGATE-MINERAL ADDITIVE COMBINATIONS CSA A A (ACCELERATED MORTAR BAR TEST) 25*25*285 mm PRISMATIC MORTAR BARS HAVE BEEN PREPARED

11 EXPERIMENTAL STUDY IMMERSED in 1 M NaOH SOLUTION at 80 C for 14 DAYS and THEIR LENGTHS MEASURED PERIODICALLY IF the EXPANSIONS GREATER THAN 0.15% (at 14 days) AGGREGATE IS CONSIDERED POTENTIALLY REACTIVE! SILICA FUME (REPLACEMENT RATIOS FOR SAND) 5-25 % (NUMBER of COMBINATIONS) 5 FLY ASH (C TYPE) SILICA FUME + FLY ASH (at same ratios) 5-30 % 5-30 % 6 6

12 Time (days) Expansion (%) ,0087 0,0616 0,1432 0,1804 0,2144 0,2523 Expansion (%) 0,3 0,25 0,2 0,15 0,1 0,05 0 expansion limit (14 days) 0, ,0087 0,1432 0,2523 0,2144 0, Time (days) RELATIONSHIP BETWEEN EXPANSIONS OF CONTROL SPECIMENS (Without Mineral Additives) AND TIME

13 0,25 Control mix 5 % silica fume 10 % silica fume 15 % silica fume 20 % silica fume 25 % silica fume Expansion (%) 0,2 0,15 0,1 0,05 expansion limit (14 days) Time (days) TIME DEPENDENT EXPANSIONS OF CONTROL MIX AND MORTAR BARS WITH DIFFERENT AMOUNTS OF SILICA FUME

14 Expansion (%) 0,35 0,3 0,25 0,2 0,15 0,1 0,05 0 expansion limit (14 days) Time (days) Control mix 5 % fly ash 10 % fly ash 15 % fly ash 20 % fly ash 25 % fly ash 30 % fly ash TIME DEPENDENT EXPANSIONS OF CONTROL MIX AND MORTAR BARS WITH DIFFERENT AMOUNTS OF FLY ASH

15 Expansion (%) 0,35 0,3 0,25 0,2 0,15 0,1 0,05 0 expansion limit (14 days) Time (days) Control mix 2.5 % silica fume % fly ash 5 % silica fume + 5 % fly ash 10 % silica fume + 10 % fly ash 7.5 % silica fume + 7.5% fly ash 12.5 % silica fume % fly ash 15 % silica fume + 15 % fly ash TIME DEPENDENT EXPANSIONS OF CONTROL MIX AND MORTAR BARS WITH DIFFERENT AMOUNTS OF SILICA FUME and FLY ASH

16 Expansion (%) 0,35 0,3 0,25 0,2 0,15 0,1 0, Mineral admixture ratio (%) expansion limit (14 days) Control mix Silica fume Fly ash Silica fume+fly ash AVERAGE EXPANSION VALUES OF ALL SPECIMENS INCLUDING CONTROL MIX at 14 DAYS

17 CONCLUSIONS TEST RESULTS INDICATE THAT WHEN SILICA FUME AND/OR FLY ASH ARE USED IN SUFFICIENT AMOUNTS, EXPANSION DUE TO ASR MAY BE DECREASED TO HARMLESS LEVEL. CLASS C FLY ASH IS NOT EFFECTIVE UNLESS USING HIGH REPLACEMENT LEVELS. BELOW 15% OF INCORPORATION OF FLY ASH CAUSED SWELLING. WHEREAS, WHEN EXCEEDING THIS RATIO, THE EXPANSION VALUES DECREASED. USING 30% FLY ASH AS A SAND REPLACEMENT REVEALED A REDUCTION OF 66% IN TERMS of EXPANSIONS IN COMPARISON WITH THE CONTROL SPECIMENS.

18 CONCLUSIONS PARTIAL REPLACEMENT OF REACTIVE SAND BY SILICA FUME REDUCED THE EXPANSIONS OF MORTAR BARS IN ALL COMPOSITION (FOR EXAMPLE, INCORPORATING 10% SILICA FUME REDUCED THE EXPANSIONS BY 90% IN COMPARISON WITH THE CONTROL SPECIMENS). THE DISADVANTAGES OF CLASS C FLY ASH IN TERMS OF CONTROLLING ASR MAY BE COMPENSATED BY INCORPORATING RELATIVELY SMALL QUANTITIES OF SILICA FUME. A FURTHER RESEARCH WILL BE PLANNED FOR COMBINATIONS OF FLY ASH AND SILICA FUME WITH DIFFERENT REPLACEMENT RATIOS.

19 THE EFFECT OF SILICA FUME AND FLY ASH ON ALKALI-SILICA REACTION (ASR) Kamile TOSUN Halit YAZICI Bülent BARADAN Civil Engineering Department