The present invention is directed to a cement admixture composition and a resultant cement which is capable of inhibiting shrinkage of and cracking with respect to cast cement structures.

One of the major disadvantages of conventional cement compositions is that they tend to shrink during drying of the composition. This shrinkage results in cracks and other defects in the resultant structure. The cracks cause both appearance and physical defects to the structure. Although the magnitude of the shrinkage is normally small, it is of extreme importance. Such shrinkages give rise to internal and external stresses which cause formation of cracks. The largest changes normally take place during the early life of the structure. The resultant crack formation to release the stresses of the formation provides means of seepage of water in and through the structure. Water entry further deteriorates the structure through freeze-thaw pressures exerted by the water on the cement composition and by corrosion of metal reinforcing elements within the structure.

Various attempts have been made without success to vary the cement composition, per se, to overcome the shrinkage problem. These attempts included varying the properties of the cement, varying the methods of manufacture of a concrete mix and varying the ballast material used to form the resultant concrete composition. None of these attempts have resulted in a satisfactory solution.

Various admixtures have been proposed as useful in reducing shrinkage and the resultant cracking. For example Japanese Laid-Open Applications 81/37259 and 87/10947 disclose the use of alcohol-alkylene oxide and alkylphenol-alkylene oxide adducts as useful for this purpose. It was found that these materials must be used in large dosages which causes their usage to be expensive in order to provide the desired result. Lower alcohols as C ₄ -C ₆ alkyl alcohols (See U. S. Patent 5,181,961) have also been suggested but these materials tend to be readily leached out by wet conditions which may be encountered. Further, such lower alcohols have high vapor pressures at ambient conditions and, therefore, are difficult to handle. Further, various primary polyols have been suggested as a crack control agent. For example, Japanese Laid- Open Application 55-027819 discloses primary diol compounds of the formula RC(CH ₂ θH) ₂ CH ₃ , such as neopentylglycol, as being useful to inhibit shrinkage; EPA 308,950 discloses terminal hydroxyl containing compounds of the formula C _n H _2n (OH) ₂ with the value of n being 5-10 as suitable for reduction of shrinkage; Japanese Laid-Open Application 06-072749 discloses 1,6 hexanediols for the desired purpose; and Japanese Laid Open Application 06-072748 disclose 2,2,-dimethyl-1,3- propanediol (neopentylglycol) for the desired purpose. It is highly desired to provide a cement additive which is capable of reducing shrinkage and resultant cracking of the cast cement composition structure to high degrees.

Biimmnry «*F the Invention

The present invention is directed to a cement admixture composed of at least one secondary/tertiary hydroxyl group containing compound represented by the Formula I:

R R

R' - C - (CH ₂ ) _n " C - R' (I)

OH OH wherein each R independently represents hydrogen or ^c _l ~ ^c ₂ alkyl; each R* independently represents a Cx - C alkyl and n is an integer of 1 - 2.

The inclusion of from about 0.8 to 4 weight percent of the subject compounds based on the cement content of the treated composition unexpectedly provides an enhanced degree of reduction of shrinkage and inhibition of resultant cracking.

Detailed Description

It has been presently unexpectedly found that compounds of Formula I, as fully disclosed below, are capable of providing enhanced inhibition of shrinkage and resultant stress cracks normally encountered in cement compositions.

Cement compositions undergo a sequence of stages during its complete curing process. From the initial hydration until set, the mass undergoes certain dimensional changes including plastic shrinkage. The mass, however, may overcome and correct for the stresses which occur at this stage. However, subsequent to set, the mass undergoes further dimensional changes which are called dry changes including dry shrinkages. Although such dry shrinkage is small in magnitude, it gives rise

to internal and external stresses which result in permanent cracks and deformations to the mass. Such cracks provide the means for seepage of water through the mass and for deterioration of the formed structure from forces encountered during freeze-thaw cycling of the entrapped water.

It has been unexpectedly found that shrinkage of structure composed of a cement composition can be substantially inhibited by the introduction of an admixture composed of at least one polyol having secondary and/or tertiary hydroxyl groups and represented by the formula

R R

I I

R- - C - (CH ₂ ) _n " C - R' (I) OH OH

wherein each R independently represents hydrogen atom or a Ci-C ₂ alkyl group; each R' independently represents a C ₁ -C ₂ alkyl group; and n represents an integer of 1 or 2. Each C ₁ -C ₂ alkyl group, i.e. methyl or ethyl, may be common to all the groups or may be different. Higher alkyl groups could be used but do not provide an admixture compound which is water soluble and, therefore, readily dispersible in the hydration water used in forming the cement structure. The preferred compound of Formula I is 2-methyl-2,4-pentanediol.

The present secondary/tertiary polyols represented by Formula I can be readily dispersed in aqueous media or formed into aqueous solutions. The polyols can be used as an admixture which is introduced into the cement composition at the job site as part of the water of hydration or at the ready-mix batching plant. Alternately, the polyol can be substantially uniformly mixed with a dry particulate cement composition. The

mixture can be formed in known manners, such as by spraying the neat polyol or concentrated aqueous solution of the polyol onto a hydratable cement composition to provide a powdery solid product which can be used at a later time to form a mortar, cement or concrete composition.

The present polyol should be used in at least about 0.8 percent, preferably from 1 to 3 percent, by weight based on the weight of hydraulic cement. Thus, when the polyol of the present invention is introduced into a hydraulic cement composition as part of the water component, it should be introduced in sufficient amount to provide at least 0.8 weight percent, preferably from 1 to 5 weight percent and most preferably from 1 to 3 weight percent based on the hydraulic cement component of the cement composition. When made part of a powder solid particulate hydraulic cement product, such product should be a substantially uniform (as uniform as practical using conventional processing) admixture having a weight ratio of from 95:5 to 99.2:0.8.

The presently described polyols have been found to inhibit dry shrinkage to a high degree in a variety of cement compositions such as pastes (cement and water) ; mortars (cement, sand and water) ; and concrete (cement, sand, gravel and water) . The cements found suitable are hydraulic cements such as ordinary portland cements (e.g. ASTM Type I) , special portland cements (e.g. high early strength portland cements and moderate heat portland cement) , blast furnace slag cement, portland fly ash cement as well as high aluminous cement, blended cements (hydraulic cement containing 5 - 80% fillers or clinker substitutes which do not provide enhancement of 28 day compressive strength values) and the like.

In the preparation of a cement composition of the invention, aggregates such as coarse aggregate (e.g. gravel) , fine aggregate (e.g. sand) , pumice and burned perlite may be used in known manners according to the specific application. Further, conventional water- reducing agents, air-entraining agents, expansive agents, shrinkage-reducing agents other than the present invention, and other known admixtures for mortar or concrete may be jointly used. Examples of known additives for mortar and concrete include set accelerators, such as metal chlorides (e.g. calcium chloride) ; hardening retarders such as saccharides, starches, hydroxy carboxylic acids and glycerol; and corrosion inhibitors for reinforcing steel, such as sodium nitrite and calcium nitrite. The amount of such an optional additive are conventionally added to cement in from 0.01 to 5 wt % based on the weight of the cement.

The amount of water to be added according to the invention is not critical as long as it is sufficient to effect hydration. The water/cement ratio is usually about 0.3 to 0.6, and preferably from 0.35 to 0.5. It has been found that the present admixture provides a further enhanced cement composition when used in combination with a water-reducing agent. Although the secondary/tertiary polyols described above can be used alone and provides both drying shrinkage inhibition and permits reduction in water, the composition when having both the subject polyols and water-reducing agent provides enhanced properties. Examples of suitable, water-reducing agents are naphthalene sulfonate- formaldehyde condensates, ligninsulfonates, melamine sulfonate-formaldehydes, polyacrylates and the like. Preferred water reducing agents which aid in providing an

enhanced cement composition structure are polyacrylic acid esters of poly(C ₂ ~C ₃ oxyalkylene) ether alcohols or polyols such as described in JP 90/0078972 and JP 90/0007901; and copolymers of maleic anhydride and alkenyl ether alcohols. The amount of such water reducing agent to be used can range in from 0.05 to 5 weight percent based on the cement content of the formed composition.

When the subject polyols and water reducing agents are used in the preferred combination, the weight ratio of these respective components should be within the range of 100:1 to 1:6 and preferably from 10:1 to 1:2.

The water-reducing agent can be added to the cement composition in ordinary manners, as part of any other admixture or with the present drying shrinkage control agent when added to the mixture of cement, aggregate and water.

It has been found that when the present secondary/tertiary polyol compound is made a part of the initial mixture of cement composition, the formed structure exhibits a decrease in shrinkage and corresponding stress cracks over untreated compositions. Thus, the present invention provides a method for inhibiting the formation of cracks and the like defects due to shrinkage. This method requires the formation of a substantially uniform mixture of cement, sand, aggregate (optional) and water in conventional wt. ratios, such as 20-25: 35-45: 80-55: 5-15 with at least one compound of Formula I. The cement to Formula I ratio being from 95:5 to 99.2:0.8 preferably 95:5 to 99:1.

The mixture preferably contains a combination of Formula I compound and a water-reducing agent. The resultant mixture is cast into a shaped form and permitted to cure to result in a desired shaped article.

The drying shrinkage inhibiting agent of Formula I can be added either to a dry cement or to a mixture of cement and other appropriate components forming the desired cement composition. Because the present admixture polyols are low vapor pressure, high boiling liquid, they can be readily handled and stored without concern of evaporation and lack of potence at time of use. Thus, the present polyol shrinkage reducing agent can be either dry mixed with the cement powder, or spray applied to the cement powder with further mixing. When the cement composition is a cement paste, the cement composition can be prepared by using a cement having the subject agent premixed therein or by adding a prescribed amount of the shrinkage-reducing agent as part of the water which is mixed with the cement. If the cement composition is a mortar or concrete, they may be formed using a preformed cement/agent product or a composition of the shrinkage reducing agent in an aqueous solution, emulsion or dispersion may be first prepared and then mixed with cement and aggregate as part of the water of hydration, or a given amount of the shrinkage-reducing agent can be added to a mixture of cement, water, and aggregate while they are being stirred.

The cement composition may be cured using any of the atmospheric, wet air, water, and/or heat-accelerated

(steam, autoclave, etc.) curing techniques. If desired, two or more such techniques may be combined. The curing conditions may be the same as conventionally used.

The following examples are given for illustrative purposes only and are not meant to be a limitation on the claims appended hereto. All parts and percentages are by weight unless otherwise indicated. The examples given below utilize a micro-concrete mix formed from a mixture of aggregate sands having a particle size distribution

which is proportional to and reflects that of standard concrete aggregate mix (sand and gravel) .

Example l

A series of micro-concrete samples were formed according to the following procedure:

1800 parts of Type I portland cement was blended with a mixture of the following ASTM graded aggregates: 1069 parts of F-95 sand, 972 parts of C-109 sand, 972 parts of C-185 sand and 1847 parts of 15-S sand. The dry blending was conducted in a Hobart mixer for approximately five (5) minutes to attain a uniform blend having an aggregate to cement weight ratio of 2.7. To the blend was added 756 parts of deionized water (water to cement weight ratio of 0.42) into which an appropriate amount (See Table I below) of 2-methyl-2,4-pentanediol had been previously dissolved. The blend was mixed in the Hobart mixer for approximately nine additional minutes to form a micro-concrete. (A hydraulic cement/aggregate mix which uses smaller proportioned aggregates to simulate concrete.)

Each of the formed micro-concrete compositions were poured into four to five prism molds with a square (1 inch by 1 inch) cross-section. The inner surface of each mold was pretreated to provide non-stick surfaces. Each prism was evenly filled using a vibrating table and by screeding off (leveling off with a knife blade) any excess mix from the surface. Each series of molds was transferred to a fog chamber which was maintained at room temperature and 100% relative humidity to permit the sample to be initially moist cured for twenty-four hours. The samples were then removed from the fog chamber, demolded and placed

in an environmental chamber maintained at 50% relative humidity and 22°C to proceed with dry curing. The length of each prism was periodically measured using a length comparator according to ASTM C-490-89 test procedure. The above was repeated using varying amounts of the secondary/tertiary polyol, 2-methyl-2,4-pentanediol. Each series was run for twenty-eight days. The results shown in Table I below show that a substantial reduction in shrinkage (ΔL/L) was attained when the subject polyol was present in dosages of the present invention (Samples 4, 5 and 6) .

Table I

Sample # Dosage ΔL/fc x.10 ⁶ % Reduction ( t. %) ("/in) in Shrinkage

1 0 669 0

2 0.1 732 -9

3 0.5 648 4

4 1.0 444 34

5 2.0 340 49

6 4.0 210 69

Example II

A second series of experiments were conducted to compare, on a back-to-back basis, the effectiveness of a subject secondary/tertiary polyol (exemplified by 2- methyl-2,4-pentanediol) to that of various primary diols. Each of the series of samples were formed in the same manner as described above in Example I. In addition, a second series was formed in the same manner except that the samples were permitted to remain under moist cure conditions for seven (7) days prior to demolding and dry curing.

The resultant data given in Table II below shows that the secondary/tertiary diol of the present invention provides consistently enhanced shrinkage reduction over various primary/terminal diols of similar molecular weights.

Table II

Αlaknediol Dose (wt. %) % Redn in Shrinkage % Redn in Shrinkage (Dry Cure) (Moist Cure)

2-methyl-2,4-pentanediol 1 32 33

2 45 46

2-methyl-l,3-propanediol 1 16 16

2 23 36

1,5 Pentanediol 2 18 46

1,4 Butanediol 2 -8.0 15

Example III

A series of examples were prepared of a concrete having a cement factor of 611 pounds per cubic yard. The concrete was formed from 611 parts portland cement, 1270 parts sand, 1750 parts aggregate and water at a water to cement ratio of 0.51. The concrete was partitioned into samples to which 2-methyl-2,4-pentanediol (MPD) was added as part of the mix in amounts as shown in Table III below. In addition, a concrete of the same formulation as above was prepared except that the MPD was added in combination with naphthalene sulfonate-formaldehyde condensate water reducing agent and the water to cement ratio was reduced to 0.41 to obtain the same slump as developed by the above samples. The results are shown in Table III below.

Cast samples were cured at 100 percent relative humidity for one or seven days. Shrinkage was measured on the samples according to ASTM-C-490-89 test procedures.

Table III

Additive Dosage w/c Slump Δ / K 10 ⁶ % Reduction in Shrinkage

1 Day 7 Days 1 Day 7 Days

None 0 0.51 7.5 855 815

MPD* 2% 0.51 9 640 590 25 28

MPD* 1% 0.51 9 780 765 9 6

MPD* 2/0.5 0.41 9 550 510 36 37 + NSFC**

* 2-methyl-2 , 4-pentanediol ** Naphthalene sulfonate-formaldehyde condensate

EXAMPLE IV

Micro concrete samples were formed according to the procedure described in Example I above. The sand to cement ratio was 2.7 and the water to cement ratio was 0.42. 2-methyl-2,4-pentanediol was added as described above in Example I. Each mix was cast into a stainless steel O ring mold with a 12" outer ring and an 8" inner ring formed from 0.5" thick Schedule 80 carbon steel. The samples were cured for six hours at 100% relative humidity and then demolded from the outer ring while retaining the inner ring of the mold in place. The samples were dried at 50% relative humidity until cracking occurred. The time (days) for the restrained sample to crack was observed and reported in Table IV below.

TABLE IV

Restrained Shrinkage

Restrained Shrinkage

Additive Dosage Days to Crack

10

MPD 0.1 11

MPD 0.5 11

MPD 1 20

MPD 2 28

MPD 4 >28