Low-density high-strength concrete and related methods
A low-density, high-strength concrete composition that is lightweight and self-compacting or non-self-compacting, 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 a lower density, such as an oven-dried density as low as 40 lbs./cu.ft. 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 hydraulically settable lightweight concrete composition that cures to a cured composite following addition of water, said composition comprising:
one or more cementitious materials, where the cementitious material comprises one or more natural pozzolans;
an aggregate mix composed of individual particles that are substantially volumetrically stable and non-absorbent, wherein the aggregate comprises a first lightweight aggregate and a second lightweight aggregate;
said first lightweight aggregate comprising hollow glass microspheres;
said second lightweight aggregate comprising polymer beads; and
said polymer beads being solid and having a median size of greater than about 150 μm.
2. The hydraulically settable lightweight concrete composition of claim 1 , wherein the natural pozzolans are class N natural pozzolans.
3. The hydraulically settable lightweight concrete composition of claim 1 , wherein the cementitious material further comprises one or more of fly ash, silica fume, and calcium carbonate.
4. The hydraulically settable lightweight concrete composition of claim 1 , wherein the cementitious material further comprises calcium carbonate.
5. The hydraulically settable lightweight concrete composition of claim 1 , wherein said polymer is a co-polymer.
6. The hydraulically settable lightweight concrete composition of claim 1 , wherein said first and second lightweight aggregates have a median size; and a ratio of the median sizes of said second and first lightweight aggregate is at least about 3.
7. The hydraulically settable lightweight concrete composition of claim 1 , wherein the density of the polymer forming the bead is between about 0.8 and 1.4.
8. The hydraulically settable lightweight concrete composition of claim 7 , wherein said density is about 1.06.
9. The hydraulically settable lightweight concrete composition of claim 1 , wherein said first and second lightweight aggregate each have a volume; and a ratio of the volumes of said first and second lightweight aggregate is between about 0.3-6.
10. The hydraulically settable lightweight concrete composition of claim 9 , wherein said ratio is between about 0.5-2.
11. The hydraulically settable lightweight concrete composition of claim 1 , wherein said one or more cementitious materials and said aggregate mix are present in an amount effective to achieve a target density in said cured composite of not more than about 125 lb./cu.ft.
12. The hydraulically settable lightweight concrete composition of claim 1 , wherein said first lightweight aggregate has a median size between about 55-85 μm.
13. The hydraulically settable lightweight concrete composition of claim 1 , wherein said first lightweight aggregate has a 90% crush survival rate below about 350 psi.
14. The hydraulically settable lightweight concrete composition of claim 1 , further comprising water; said water, one or more cementitious materials and aggregate mix present in amounts effective to achieve a target plastic density in said composition of not more than about 135 lb./cu.ft.; and wherein the composition is self-compacting.
15. A hydraulically settable lightweight concrete composition, said composition comprising:
one or more cementitious materials, where the cementitious material comprises one or more natural pozzolans;
water; and
an aggregate mix composed of individual particles that are substantially volumetrically stable and non-absorbent;
said aggregate mix comprising at least a first lightweight aggregate;
said first lightweight aggregate comprising hollow glass microspheres;
a shrinkage reducer; and
an expansive agent;
said first lightweight aggregate remaining largely unsegregated in said composition prior to curing.
16. The hydraulically settable lightweight concrete composition of claim 15 , wherein the natural pozzolans are class N natural pozzolans.