Low-density high-strength concrete and related methods
A low-density, high-strength concrete composition that is both self-compacting and lightweight, with a low weight-fraction of aggregate to total dry raw materials, and a highly-homogenous distribution of a non-absorptive and closed-cell lightweight aggregate such as glass microspheres or copolymer polymer beads or a combination thereof, and the steps of providing the composition or components. Lightweight concretes formed therefrom have low density, high strength-to-weight ratios, and high R-value. The concrete has strength similar to that ordinarily found in structural lightweight concrete but at an oven-dried density as low as 40 lbs./cu.ft. The concrete, at the density ordinarily found in structural lightweight concrete, has a higher strength and, at the strength ordinarily found in structural lightweight concrete, a lower density. Such strength-to-density ratios range approximately from above 30 cu.ft/sq.in. to above 110 cu.ft/sq.in., with a 28-day compressive strength ranging from about 3400 to 8000 psi.
1. A lightweight Portland cement-based concrete composition comprising:
one or more cementitious materials comprising 30-55% by weight of Portland cement (based on 100% total weight of concrete composition) and optionally fly ash, where (i) the fly ash, when present, is in an amount up to about 14% by weight of the lightweight concrete composition and (ii) the Portland cement is selected from Types I, IA, II, and IIA, and any combination of any of the foregoing;
an aggregate mix comprising hollow glass microspheres that are substantially volumetrically stable and non-absorbent;
a de-air entrainer;
a shrinkage reducer;
a viscosity modifier; and
polyvinyl alcohol fibers,
wherein the lightweight concrete composition has a compressive strength after 28 days as measured by ASTM C 39 of at least about 2500 psi, and an R-value of at least 0.25 when measured according to ASTM C177 at a 1″ thickness of the lightweight concrete composition.
2. The lightweight concrete composition of claim 1 , wherein the shrinkage reducer comprises calcium oxide, calcium sulfo-aluminate, or any combination of any of the foregoing.
3. The lightweight concrete composition of claim 1 , wherein the de-air entrainer is present in an amount of about 8.5 to 14.2 oz. per 100 lbs. of cementitious materials.
4. The lightweight concrete composition of claim 1 , wherein the concrete composition has an oven-dried density of about 36 to about 55 lb/ft 3 as measured according to ASTM C567.
5. The lightweight concrete composition of claim 1 , wherein said glass microspheres have a specific gravity of about 0.15, and said glass microspheres have a 90% survival rate at a pressure of about 300 psi.
6. The lightweight concrete composition of claim 1 , wherein the concrete composition has a compressive strength-to-density ratio of about 71.2 to about 97.1, where the compressive strength is measured in psi according to ASTM C39 after 28 days and the density is measured in lb/ft 3 according to ASTM C567.
7. The lightweight concrete composition of claim 1 , wherein the concrete has a ring test score, as measured by ASTM C1581, of at least about 10.1.
8. The lightweight concrete composition of claim 1 , wherein the compressive strength after 28 days as measured by ASTM C39 of at least about 3800 psi.
9. The lightweight concrete composition of claim 1 , wherein the concrete composition has a compressive strength-to-density ratio of about 29.8 to about 62.5, where the compressive strength is measured in psi according to ASTM C39 after 7 days and the density is measured in lb/ft 3 according to ASTM C567.
10. The lightweight concrete composition of claim 1 , further comprising gravel.
11. The lightweight concrete composition of claim 1 , wherein the concrete composition has (i) a compressive strength-to-density ratio of about 48.5 to about 97.1, where the compressive strength is measured in psi according to ASTM C39 after 28 days and the density is measured in lb/ft 3 according to ASTM C567, and (ii) an oven-dried density of about 36 to about 55 lb/ft 3 as measured according to ASTM C567.
12. The lightweight concrete composition of claim 1 , wherein the concrete composition has a compressive strength-to-density ratio of about 40.3 to about 62.5, where the compressive strength is measured in psi according to ASTM C39 after 7 days and the density is measured in lb/ft 3 according to ASTM C567.
13. The lightweight concrete composition of claim 1 , wherein the de-air entrainer is present in an amount of about 6 to 10 oz. per 100 lbs. of cementitious materials.
14. The lightweight Portland cement-based concrete of claim 1 , wherein the concrete comprises 40-55% by weight of Portland cement.
15. The lightweight Portland cement-based concrete of claim 1 , wherein the R-value is at least 0.37.
16. The composition of claim 1 , wherein the concrete composition has an oven-dried density of about 40 to about 70 lb/ft 3 as measured according to ASTM C567.
17. A method for preparing a lightweight Portland cement-based concrete composition comprising the steps of:
(a) obtaining a cementitious mixture comprising
(i) one or more cementitious materials comprising 30-55% by weight of Portland cement (based on 100% total weight of cementitious mixture) and optionally fly ash, where (A) the fly ash, when present, is in an amount up to about 14% by weight of the cementitious mixture and (B) the Portland cement is selected from Types I, IA, II, and IIA, and any combination of any of the foregoing,
(ii) an aggregate mix comprising hollow glass microspheres that are substantially volumetrically stable and non-absorbent,
(iii) a shrinkage reducer,
(iv) a viscosity modifier to inhibit segregation of the glass microspheres within the mixture,
(v) polyvinyl alcohol fibers, and
(vi) water;
(b) reducing the amount of air entrained within the cementitious mixture by adding a de-air entrainer; and
(c) curing the cementitious mixture,
wherein the lightweight concrete composition has a compressive strength after 28 days as measured by ASTM C39 of at least about 2500 psi, and an R-value of at least 0.25 when measured according to ASTM C177 at a 1″ thickness of the lightweight concrete composition.
18. The method of claim 17 , wherein said hollow glass microspheres remain largely unsegregated in said cementitious mixture prior to curing.
19. The method of claim 17 , wherein step (b) comprises adding a sufficient amount of de-air entrainer to achieve a plastic air content within the cementitious mixture of between about 2% and 7%.
20. The method of claim 17 , wherein, prior to curing, the cementitious mixture has a target plastic density of not more than about 100 lb./ft 3 .
21. The method of claim 17 , further comprising the step of increasing the resistance of the cementitious mixture to cracking during curing by adding a shrinkage reducer to the cementitious material prior to curing.
22. A lightweight Portland cement-based concrete composition having a compressive strength after 28 days as measured by ASTM C39 of at least about 2500 psi, and an R-value of at least 0.25 when measured according to ASTM C177 at a 1″ thickness of the lightweight concrete composition,
wherein the composition is prepared by a process comprising the steps of:
combining, to form a mixture, (i) one or more cementitious materials comprising 30-55% by weight of Portland cement (based on 100% total weight of concrete composition) and optionally fly ash, where (A) the fly ash, when present, is in an amount up to about 14% by weight of the lightweight concrete composition and (B) the Portland cement is selected from Types I, IA, II, and IIA and any combination of any of the foregoing, (ii) an aggregate mix comprising hollow glass microspheres that are substantially volumetrically stable and non-absorbent, (iii) a de-air entrainer, (iv) a shrinkage reducer, (v) a viscosity modifier, (vi) polyvinyl alcohol fibers, (vii) hydration stabilizer, and (viii) water; and
curing the mixture,
wherein the mixture, prior to curing, has (i) a water to cement ratio of about 0.15-0.35 and (ii) a slump as measured by ASTM C143 of 5 to less than 40.
23. The lightweight concrete composition of claim 22 , wherein the concrete composition has an oven-dried density of about 36 to about 55 lb/ft 3 as measured according to ASTM C567.
24. The lightweight concrete composition of claim 22 , wherein the concrete composition has a compressive strength-to-density ratio of about 71.2 to about 97.1, where the compressive strength is measured in psi according to ASTM C39 after 28 days and the density is measured in lb/ft 3 according to ASTM C567.
25. The lightweight concrete composition of claim 22 , wherein the de-air entrainer is present in an amount of about 8.5 to 14.2 oz. per 100 lbs. of cementitious materials.
26. The concrete composition of claim 22 , wherein the mixture comprises a sufficient amount of de-air entrainer to achieve a plastic air content within the mixture of between about 2% and 7% by volume.
27. The concrete composition of claim 22 , wherein (a) the one or more cementitious materials comprise at least about 535 lb/yd 3 of Portland cement in the concrete composition, and (b) the total cementitious content in the concrete composition is 825 lb/yd 3 or less.
28. The composition of claim 22 , wherein the concrete composition has an oven-dried density of about 40 to about 70 lb/ft 3 as measured according to ASTM C567.