Superplasticizer and workabilty retention agent for concrete and mortar with limestone calcined clay cement

Abstract

The invention discloses a composition of superplasticizer and workability retention agent (100) for increasing the workability of limestone calcined clay cement binder for concrete and mortar. The composition includes sulphonated naphthalene formaldehyde (104) ranging from 5 to 70%, sodium hexametaphosphate (106) ranging from 5 to 70%, sodium carbonate ranging from 0.1 to 15% and sodium silicate (meta) nonahydrate ranging from 0 to 85% proportion by weight. The weight ratio of sodium hexametaphosphate to sodium carbonate is in the range 4.5 to 5. The superplasticizer is added in a dosage range of 0.05 to 5% of weight of the limestone calcined clay cement binder. The workability loss is reduced to less than 8% for water to binder ratios 0.35 and 0.40 on adding the superplasticizer.

Description

SUPERPLASTICIZER AND WORKABILTY RETENTION AGENT FOR CONCRETE AND MORTAR WITH LIMESTONE CALCINED CLAY CEMENTCROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This application claims priority to Indian Patent Application No. 202441012387 entitled SUPERPLASTICIZER AND WORKABILTY RETENTION AGENT FOR CONCRETE AND MORTAR WITH LIMESTONE CALCINED CLAY CEMENT, filed on 21 February, 2024.FIELD OF THE INVENTION

[0002] The invention generally relates to construction materials and in particular to additive for limestone calcined clay cement.DESCRIPTION OF THE RELATED ART

[0003] Limestone calcined clay cement (LC3) is composed of ordinary Portland cement, calcined clay, and limestone and is prepared as per IS: 18189-2023. The concrete is prepared by mixing LC3, aggregates, and water. The concrete and mortar system made with LC3 loses workability rapidly within the first few hours of mixing. The workability is measured generally using a slump test or flow table test for concrete. The slump value reduces by about 40 to 60% within the first 1 to 2 hours from mixing for a normal LC3 concrete having presently available superplasticizers (SP). These superplasticizers are mostly made of polycarboxylate ether (PCE) as a primary compound. Sulphonated Naphthalene formaldehyde (SNF) is used to reduce the water demand of the concrete and act as a superplasticizer for normal concrete. However, SNF is observed not to be very effective for LC3-based concrete.

[0004] Various publications have attempted to address the challenges. EP2970007B1 discloses a dry mortar composition with a prolonged open time. EP4204382A1 discloses a limestone calcined clay cement construction composition comprising a cementitious binder. CN101985391A discloses an additive for activating fly ash. US10843969B2 discloses an alkali activated natural pozzolan-based concrete containing ground granulated blast furnace slag. However, these publications do not address the challenges of increasing the workability of the cement or mortar.SUMMARY OF THE INVENTION

[0005] The present subject matter discloses a superplasticizer and workability retention agent for increasing the workability of limestone calcined clay cement binder for concrete and mortar.

[0006] According to one embodiment of the present subject matter, the superplasticizer comprises a composition of sulphonated naphthalene formaldehyde ranging from 5 to 70%, sodium hexametaphosphate ranging from 5 to 70%, sodium carbonate ranging from 0.1 to 15% and sodium silicate (meta) nonahydrate ranging from 0 to 85% proportion by weight, wherein the weight ratio of sodium hexametaphosphate to sodium carbonate is in the range 4.5 to 5. The superplasticizer is added in a dosage range of 0.05 to 5% of weight of the limestone calcined clay cement binder.

[0007] According to some embodiments, the sodium hexametaphosphate in the superplasticizer is configured to be adsorbed on the surface of calcined clay at Al3+sites and the calcium ions attach to the sodium hexametaphosphate forming a Ca-Sodium hexametaphosphate (Ca-SHMP) complex. The workability loss is reduced to less than 8% for water to binder ratios 0.35 and 0.40 on adding the superplasticizer. The mixture is usable in both dry powder form and water soluble form, the composition is configured for retardation of ettringite formation, leading to higher workability retention of limestone calcined clay cement concrete and mortar. The workability drop in terms of slump and flow value on adding the superplasticizer is limited to 5 to 10% within the first 1 to 2 hours of mixing.

[0008] This and other aspects are described herein.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The invention has other advantages and features, which will be more readily apparent from the following detailed description of the invention and the appended claims, when taken in conjunction with the accompanying drawings, in which:

[0010] FIG. 1 shows a representation of the superplasticizer for limestone calcined clay cement (LC3) binder for concrete and mortar.

[0011] FIG. 2 illustrates the results obtained for the hydration reaction of the modified SNF-based superplasticizer.

[0012] FIG. 3 shows the compressive strength of the normal SNF-based superplasticizer and modified SNF-based superplasticizer after 7 days and after 28 days.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0013] While the invention has been disclosed with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt to a particular situation or material to the teachings of the invention without departing from its scope.

[0014] Throughout the specification and claims, the following terms take the meanings explicitly associated herein unless the context clearly dictates otherwise. The meaning of "a", "an", and "the" include plural references. The meaning of "in" includes "in" and "on." Referring to the drawings, like numbers indicate like parts throughout the views. Additionally, a reference to the singular includes a reference to the plural unless otherwise stated or inconsistent with the disclosure herein.

[0015] The present subject matter describes a superplasticizer for adding to limestone calcined clay cement binder for concrete and mortar.

[0016] The invention in various embodiments discloses a composition of superplasticizer and workability retention agent 100 for increasing the workability of limestone calcined clay cement (LC3) binder 102 for concrete and mortar. FIG. 1 gives a representation of the superplasticizer. The composition comprises sulphonated naphthalene formaldehyde (SNF) 104 ranging from 5 to 70%, sodium hexametaphosphate (SHMP) 106 ranging from 5 to 70%, sodium carbonate (SC) ranging from 0.1 to 15% and sodium silicate (meta) nonahydrate (SSM) ranging from 0 to 85% proportion by weight of the superplasticizer. The weight ratio of sodium hexametaphosphate to sodium carbonate is in the range 4.5 to 5 in the superplasticizer. According to one embodiment of the invention, the superplasticizer may be added to the LC3 cement binder in the dosage range of 0.05 to 5% of the weight of the binder. The superplasticizer is a modified SNF- based superplasticizer. According to various embodiments, the superplasticizer may be added in solid form to the concrete during any mixing stage, or it can be mixed in water and added to the concrete.

[0017] In various embodiments, the sodium hexametaphosphate is configured to be adsorbed on the surface of calcined clay at Al3+sites. The calcium ions attach to the sodium hexametaphosphate, forming a Ca-Sodium hexametaphosphate (Ca-SHMP) complex. The side sulphonic groups of sulphonated naphthalene formaldehyde get attracted toward the positive calcium ions in the Ca-SHMP complex. The attached SNF chains lead to an increase in the electronegativity of the cement and clay surfaces. This leads to electrostatic repulsion between the cement particles and calcined clay particles, according to one embodiment of the invention. The dispersing effect of sodium hexametaphosphate increases with an increase in the pH of the pore solution. At higher pH, the hexametaphosphate shows a better performance. At higher alkalinity, the calcined clays are more dispersed. Sodium carbonate and sodium silicate (meta) nonahydrate increase the pH of the cement pore solution.

[0018] The dissolution of calcium and alumina ions in the LC3 cement system controls the initial hydration reaction and the workability loss. The LC3 cement system has higher C3A content, which leads to faster hydration and ettringite formation, leading to workability loss within an hour of mixing. The dissolution of calcium and aluminum governs the reaction of C3A. In the modified SNF-based superplasticizer, the sodium carbonate reacts with the calcium present in the pore solution and forms a layer of precipitate over the cement particles. On the other hand, sodium silicate reacts with alumina to retard the reaction kinetics of C3A. The composition of SNF-based superplasticizer comprising sodium hexametaphosphate, sodium carbonate and sodium silicate leads to retardation of the ettringite formation, leading to higher workability retention.

[0019] The workability drop in terms of slump and flow value is limited to 5 to 10 % within first 1 to 2 hours on adding the modified SNF based superplasticizer. The hydration is retarded and the composition acts as a retarding admixture for the first day. The modified SNF-based superplasticizer is effective in ambient tropical temperatures.EXAMPLES

[0020] Example 1: Workability retention of the modified sulfonated naphthalene formaldehyde (SNF) based superplasticizer

[0021] The workability retention is shown in the Table 1. This study has been performed with LC3 containing 55% OPC (cement), 30% calcined clay, and 15% limestone. When un-modified SNF was used, segregation was observed at higher dosages for water with binder ratio of 0.4. However, at lower dosages of 0.3 and 0.15 %, the workability reduction is more than 22%. For water to binder ratio of 0.35, the workability reduction was 20 to 30% for 0.3 to 0.8% SNF dosage.Table 1: Workability of Various Compositions of the Novel Superplasticizer

[0022] It can be observed that unmodified SNF is unable to retain the flow within an hour at lower dosages and segregate at higher dosages. The modified SNF-based SP with different proportions of SNF, SHMP, SC, and SSM is observed to reduce the workability loss to less than 8% for both water-to-binder ratios of 0.35 and 0.4. The admixture is used in both dry powder form and water solution form.

[0023] Example 2: Hydration of the SNF based superplasticizer

[0024] The hydration reaction can be altered depending on the combination ratio of the all the four constituents of the modified SNF based superplasticizer. Table 2 shows the dosage of the SNF taken and the ratio of four constituents SNF, SHMP, SC, SSM. The reaction can be altered from highly retarded (Modified 1 in Table 2) to reaction nearly equivalent to unmodified SNF (Modified 3 in Table 2) at the end of 24 hr (day 1). FIG. 2 shows the results obtained for the hydration reaction by way of heat generation of three modified SNF based superplasticizer compositions in various proportions of the constituents and the unmodified SNF. The hydration is retarded and the modified SNF based superplasticizer also acts as a retarding admixture for the first day. Workability retention is possible only with the modified SNF.Table 2: Variation of Hydration Reaction with Composition of Superplasticizer

[0025] Example 3: Compressive strength of the SNF based superplasticizer

[0026] The mechanical properties and the compressive strength are not affected on mixing the superplasticizer with limestone clay cement for concrete and mortar. FIG. 3A and 3B show the compressive strength of the normal SNF based superplasticizer and modified SNF based superplasticizer after 7 days and after 28 days, respectively.

[0027] While the invention has been disclosed with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt to a particular situation or material the teachings of the invention without departing from its scope, which should be as defined by the claims appended herewith.

Claims

We claim:

1. A composition of superplasticizer for reducing workability loss of limestone calcined clay cement binder for concrete and mortar for a period of 1-2 hours, comprising: sulphonated naphthalene formaldehyde ranging from 5 to 40%, sodium hexametaphosphate ranging from 8 to 40%, sodium carbonate ranging from 1.5 to 10% and sodium silicate (meta) nonahydrate ranging from 35% to 85% proportion by weight, wherein the weight ratio of sodium hexametaphosphate to sodium carbonate is in the range 4.5 to 5, wherein the workability loss is reduced to less than 8% for water to binder ratios 0.35 and 0.40 on adding the superplasticizer.

2. The superplasticizer as claimed in claim 1, wherein the superplasticizer is added in a dosage range of 0.05 to 5% of weight of the limestone calcined clay cement binder.

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