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 hydraulically settable lightweight concrete composition that cures to a cured composite following addition of water, said composition comprising:
one or more cementitious materials;
an aggregate mix composed of individual particles that are substantially volumetrically stable and non-absorbent;
said aggregate mix comprising at least a first and 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 said polymer is a co-polymer.
3. The hydraulically settable lightweight concrete composition of claim 1 , wherein an exterior surface of at least one of said first and second lightweight aggregate is etched by a process.
4. The hydraulically settable lightweight concrete composition of claim 3 , wherein the exterior surfaces of said first and second lightweight aggregate have been acid-etched.
5. The hydraulically settable lightweight concrete composition of claim 1 , wherein the ratio of the median sizes of said second and first lightweight aggregate is at least about 3.
6. The hydraulically settable lightweight concrete composition of claim 5 , wherein said ratio is between about 5-15.
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 1 , wherein the ratio of the volumes of said first and second lightweight aggregate is between about 0.3-6.
9. The hydraulically settable lightweight concrete composition of claim 8 , wherein said ratio is between about 0.5-2.
10. 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.
11. The hydraulically settable lightweight concrete composition of claim 1 , wherein said first lightweight aggregate has a median size between about 55-85 μm.
12. The hydraulically settable lightweight concrete composition of claim 1 , wherein said first lightweight aggregate has a 90% crush survival rate below about 350 psi.
13. The hydraulically settable lightweight concrete composition of claim 1 , wherein said aggregate mix further comprises sand and gravel and reinforcing fibers.
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. The hydraulically settable lightweight concrete composition of claim 1 , further comprising a shrinkage reducer and an expansive agent.
16. The hydraulically settable lightweight concrete composition of claim 1 , wherein the composition is non-self-compacting.
17. A lightweight concrete structure comprising a cured, matrix composite prepared by adding water to the composition of claim 1 to form a hydraulically curable composition, and allowing said curable composition to cure.
18. A hydraulically settable lightweight concrete composition that cures to a cured composite following addition of water, said composition comprising:
one or more cementitious materials;
an aggregate mix composed of individual particles comprising at least a first and 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;
said aggregate mix being substantially free of glass particles having a porous surface; and
said aggregate mix being substantially free of particles that are not substantially volumetrically stable.
19. The hydraulically settable lightweight concrete composition of claim 18 , wherein said aggregate mix is substantially free of aerogel and foamed particles.