Alkali aggregate reaction

Presentation on alkali aggregate reaction occuring in concrete

1. Alkali-Aggregate Reaction BY AKRAM AFRIDI

2. Alkali-Aggregate Reaction Is the reaction between the active mineral constituents of some aggregates and the sodium and potassium alkali hydroxide in the concrete Harmful only when it produes significant expansion

3. FORMS OF ALKALI AGGREGATE REACTIONS Alkali silica reactions alkali-carbonate reaction

4. Alkali silica reaction ALKALI-SILICA REACTIVITY (ASR) ALALKALI-SILICA REACTIVITY (ASR)KALI-SILICA REACTIVITY (ASR)

5. What is ASR? Visual symptoms network of cracks Closed or spalled joints Relative displacement cracking of concrete from alkali silica reactivity

6. Alkali silica reactions

7. Harmful Reactive Substances Some potentially harmful reactive minerals, rocks, and synthetic materials Several of the rocks listed react very slowly and may not show evidence of any harmful degree of reactivity until the concrete is 20 years old Only certain sources of these materials have shown reactivity

8. Pop outs A pop outs is the breaking away of a small fragment of concrete surface due to internal pressure that leaves a shallow typically conical depression

9. Controlling ASR Non reactive aggregates Supplementary cementing materials or blended cements Limit alkali loading Lithium based admixtures Limestone sweetening(30 % replacement reactive aggregates with crushed limestone)

10. Alkali carbonate reactions

11. Alkali carbonate reactions Influencing factors Clay contents, or insoluble residue content, in the range of 5% to 25% Calcite to dolomite ratio of approximately 1:1 Increase in the dolomite volume Small size of the discrete dolomite crystals (rhombs) suspended in the clay matrix

12. Alkali carbonate reactions Controlling ACR Selective quarrying to avoid reactive aggregates Blend aggregates according to appendix in ASTM C 1105 Limit aggregates size to smallest practical