Cementitious foam compositions

Abstract

Lightweight cementitious foams of the invention have excellent dynamic and dimensional stability due to use of foaming system comprising polycarboxylate surfactant foam generating agent, foam stabilizer (e.g., PVOH), and shrinkage reducing admixture to inhibit plastic shrinkage and micro-cracking of cement. The foaming system can be used in conventional cement mortars or concretes as well as with exemplary cementitious slurry systems of the invention, which include an expansive agent, a cross-linking agent for the foam stabilizer. Microfibers can be used in the foam, slurry, or both, to prevent micro-cracking. Cementitious foams can be made without use of autoclave or lightweight aggregates to achieve enhanced compressive strength and thermal insulation properties that compare favorably with conventional foams and insulation materials at comparable densities.

1 . A cementitious foam composition, comprising:
 (i) a polycarboxylate surfactant in an amount effective for generating foam in said composition;   (ii) a foam stabilizer comprising a polyvinyl alcohol, polyvinyl acetate, or mixture thereof, said foam stabilizer in an amount effective to stabilize the foam;   (iii) a shrinkage reducing admixture in an amount effective to reduce shrinkage in cementitious slurry after water is introduced to initiate hydration of cement;   (iv) a calcium salt in an amount effective to accelerate setting of cement in cementitious foam when water is added to initiate hydration, said calcium salt comprising calcium nitrite, calcium nitrate, or mixture thereof;   (v) a viscosity modifying agent;   (vi) a binder comprising Portland cement in an amount effective to provide a cementitious slurry when the cement is combined with water;   (vii) an expansion agent in an amount effective for expanding by chemical reaction the volume of said cementitious foam composition, said expansion agent comprising calcium oxide, magnesium oxide, calcium sulfoaluminate, or mixture thereof;   (viii) a cross-linking agent in an amount effective for cross-linking said foam stabilizer, said foam stabilizer cross-linking agent comprising a borate, a sulfate, an aluminate, or a mixture thereof; and   (ix) a plurality of microfibers in an amount effective to reduce cracking of the Portland cement when mixed with water in an amount effective to initiate hydration of the cement, said microfibers having an effective diameter of 5-50 microns and comprising cellulose, synthetic polymer, glass, or mixture thereof; and   
       said components (i) through (ix) being combined with water in amount effective to form a cementitious foam, to initiate hydration of said cement binder within the cementitious foam, and to incorporate said components into a foamed cementitious mass, structure, or article upon hardening of the cementitious foam. 
     
     
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         6 . The composition of  claim 1  wherein said composition is cured into a hardened mass or structure without the use of autoclave. 
     
     
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         11 . The composition of  claim 1  further comprising: (a) lightweight aggregate selected from the group consisting of vermiculite, expanded polystyrene, perlite, and mixtures thereof; (b) a plurality of reinforcing fibers for reinforcing the cement foam; (c) a water repellant agent; (d) particles of supplemental cementitious material or filler having an average particle size of no greater than 1 mm; (e) fine aggregate; (f) coarse aggregate; or (e) mixture of any of the foregoing components (a) through (f). 
     
     
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         16 . A composition for making a cross-linked foamed cementitious product, comprising:
 (i) polycarboxylate surfactant for generating foam when mixed with water;   (ii) a foam stabilizer comprising a polyvinyl alcohol, polyvinyl acetate, or mixture thereof;   (iii) a shrinkage reducing admixture for reducing shrinkage in a hydrating cementitious composition after water is added to initiate hydration of said composition;   (iv) a calcium salt for accelerating setting of cement in a cementitious foam when water is added to initiate hydration, said calcium salt comprising calcium nitrite, calcium nitrate, or mixture thereof;   (v) a viscosity modifying agent;   (vi) a binder comprising Portland cement;   (vii) an expansion agent for expanding by chemical reaction the volume of the cementitious foam composition, said expansion agent comprising calcium oxide, magnesium oxide, calcium sulfoaluminate, or mixture thereof;   (viii) a cross-linking agent for cross-linking said foam stabilizer, said foam stabilizer cross-linking agent comprising a borate, a sulfate, an aluminate, or a mixture thereof; and   (ix) a plurality of microfibers operative to reduce cracking of the Portland cement when it is mixed with water in an amount effective to initiate hydration of the cement, said microfibers having an effective diameter of 5-50 micros and comprising cellulose, synthetic polymer, glass, or mixture thereof.   
     
     
         17 . The composition of  claim 16  further comprising water in an amount effective to initiate hydration of said binders. 
     
     
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         22 . The composition of  claim 16  further comprising incorporating fine aggregate, coarse aggregate, or mixture thereof. 
     
     
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         25 . The composition claim of  16  wherein said components (i)-(iv) are provided as a separate first foam system and components (v)-(ix) are provided as a separate cementitious slurry system. 
     
     
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         27 . The composition  claim 16  further comprising (a) lightweight aggregate selected from the group consisting of vermiculite, expanded polystyrene, perlite, and mixtures thereof; (b) a plurality of reinforcing fibers for reinforcing the cement foam; (c) a water repellant agent; (d) particles of supplemental cementitious material or filler having an average particle size of no greater than 1 mm; (e) sand; (f) coarse aggregate; or (g) mixture of any of the foregoing components (a) through (f). 
     
     
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         29 . The composition of  claim 1  being molded or shaped into a three-dimensional shape. 
     
     
         30 . The composition of  claim 1  being sprayed against a surface or substrate. 
     
     
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         50 . A composition for generating a foamed cementitious material, comprising when combined with a hydratable cementitious slurry:
 (i) a polycarboxylate surfactant in an amount effective for generating foam when combined with a hydratable cementitious slurry;   (ii) a foam stabilizer comprising a polyvinyl alcohol, polyvinyl acetate, or mixture thereof, said foam stabilizer in an amount effective to stabilize the foam;   (iii) a shrinkage reducing admixture in an amount effective to reduce shrinkage in the cementitious material after water is introduced to initiate hydration of cement;   (iv) a calcium salt comprising calcium nitrite, calcium nitrate, or mixture thereof; and   (v) optionally a viscosity modifying agent, microfibers for reducing shrinkage in a cementitious composition, or a mixture thereof.   
     
     
         51 . The composition of  claim 50  comprising a plurality of microfibers to reduce cracking in a foamed cementitious material after the cement is combined with water to initiate hydration of the cement, said microfibers having an effective diameter of 5-50 microns and being comprised of cellulose, synthetic polymer, glass, or mixture thereof. 
     
     
         52 . The composition of  claim 50  further comprising an expansion agent. 
     
     
         53 . The composition of  claim 50  further comprising a cross-linking agent for said foam stabilizer.