Preparation And Evaluation Of Some Water Solublepoly Condenstion Products Based On Amino_s_triazine As Concrete Admixture :

Samah Said Ragab Atia Al_marsy

Admixtures for concrete are defined as materials other than hydrauliccement, water, or aggregates that are added immediately before or duringthe mixing. Admixtures are added to modify the properties of fresh orhardened concrete in such away to be more suitable or economic for thejob.Chemical admixtures are classified into: water reducers, retarders,accelerators and superplastizers.Admixtures are very important in industry because they increase theworkability (water reducing agent), while other kinds increase or decreasethe setting time which give more freedom for the transportation of theconcrete or cement pastes.In this investigation the MSF was prepared according to the four stepsmethod. In this method the polymers were formed through (a)hydroxymethyltion of melamine by formaldehyde giving trimethylolmelamine; (b) sulfonation of one methylol group of the product by sodiumbisulfite giving sulfonated methylol melamine; (c) low pH condensation;(d) highpH rearrangement givingmelamineformaldehyde sulfonate .The MUSF was prepared by the same manner where the melaminemolecule replaced by melamine/urea, (111) in the first step, then thesulfonation occurred in the second step. The product is undergoing low pHcondensation and high pH rearrangement at the same vessel andconditions.-137-__________________ Summary and ConclusionCement pastes were made, using different admixtures dosages such as,0.00, 0.25, 0.50, 0.75 and 1.00 mass% of cement. These admixtures wereprepared in laboratory such as;melamine sulfonate formaldehyde (MSFj) (M : S03 : F; I : 1.22 : 2.58),melamine sulfonate formaldehyde (MSF2) (M : S03 : F; 1 : 1.22 : 5.56),melamine sulfonate formaldehyde (MSF3) (M : S03 : F; 1 : 0.4 : 1.4),melamine sulfonate formaldehyde (MSF4) (M : S03 : F; 1 : 0.5 : 4) andmelamine urea sulfonate formaldehyde (MUSF).The water of consistency, initial and final setting time, rheologicalproperties, electrical conductivity, compressive strength, bulk density,chemical combined water content, gel/space ratio, DTA and IRspectroscopywere under taken.The main conclusions derived from this investigation can besummarized as the following:1- The reduction in the water of consistency increases in presence ofdifferent dosage of the admixture, this reduction was 33.33, 34.33,14.33, 8.9 and 7.67% for 1.00% dose of (MSF[), (MSF2), (MSF3),(MSF4) and (MUSF), respectively. At 0.25 mass% dosage, thereduction in the water of consistency was 11,6.67,4.33, I and 2.23%for the above admixture respectively. All prepared admixtures act aswater reducing agents.In respect of initial and final setting time of cement paste admixed withmelamine sulfonate formaldehyde (MSF1), it is found that the initialsetting time is retarded with the admixture content. The amount of themelamine sulfonate formaldehyde (MSF I) reduces the final setting time, itacts as accelerating admixture and superplasticiser.-138-__________________ Summary and ConclusionThe initial and final setting time of the cement pastes using differentdosages of melamine formaldehyde sulfonate (MSF2) show retardationeffect.It can be concluded that the prepared (MSF2) is retarding as well aswater reducer.The initial and final setting time are retarded by the addition ofmelamine sulfonate formaldehyde (MSF3). Also, as the amount of (MSF3)increases up to 0.50% the initial setting time is accelerated and thenretarded at 0.75% and 1.00%. So, it is concluded that (MSF3) is acted asretarder and water reducer. MSF4 shows the same trend of (MSF2).The initial setting time is accelerated by the addition of melamine ureasulfonate formaldehyde (MUSF). As the dosage of admixture increasesthe initial setting time decreases. By increasing the amount of (MUSF) thefinal setting time is elongated. Also, it can be concluded that (MUSF) isacted as retarder and water reducer.2- It is found that as the amount of admixtures increases the fluidity ofpastes sharply increases. Also, it is found that (MSF2) gives thehighest fluidity of cement pastes at all dosages. This means that(MSF2) is the optimum superplasticizer which gives higher fluidity ofcement pastes than the other superplasticizers.3- The combined water contents of the cement pastes mcrease withcuring time for all admixtures dosages, due to the continuoushydration. As the amount of (MSFj), (MSF2), (MSF3) and (MSF4)increases the combined water content decreases, this is mainly due tothe reduction of mixing water which effects the rate of hydration.1.00% (MUSF) gives the highest combined water contents at all ages.-139-__________________ Summary and ConclusionThis means that 1.00% is the optimum dose of this admixture whichgives higher rate of hydration but lower than the control cementsample.4- The gel/space ratio of the cement pastes increase with curing time forall admixtures dosages. This is due to the increase of the amount ofhydration products. Increase of the dosages of MSF] and MSF2 thegel/space ratio increases. As the dosages of MSF] and MSF2 increasethe water of consistency and the total porosity decrease. MSF2 giveshigher gel/space ratio values than those with MSF 1, these results are ina good agreement with the amount of water reduction. The gel/spaceratio of MSF3 and MSF4 decreases consequently the compressivestrength values. 0.5% of MSF3 is higher than 1.0%, this is due to theretardation effect MSF3. As the hydration time increases the gel/spaceratio increases up to 1.0 mass% at 90 days. At early ages (15 min up toone day) it was shown that the gel/space decreases with the amount ofMUSF dosages. At later ages (3 days up to 90 days) it was shown thatthe gel/space ratio increases with the dosages of MUSF. This is due tothe production of more dense and close-textured structure of thecement pastes.5- The bulk density of the cement pastes increases with curing time forall admixture dosages. Obviously, as the amount of (MSF]), (MSF2),(MSF3) and (MSF4) increases the bulk density increases. Also, the0.25% and 0.75% (MUSF) have higher bulk density than the otherdosages.6- The compressive strength of the cement pastes increases with curingtime for all admixtures dosages. This mainly due to the increase of theamount of hydration products especially Tobermorite - like gel-140-___________________ Summary and Conclusion(CSH). As the amount of MSFj, MSFz and MSF4 increases thecompressive strength increases due to the decrease of the mixingwater. The decrease in mixing water decreases the total porosity andimproves the compressive strength. 0.75% MSF3 gives the highervalues of the compressive strength at all ages. As the content of MSF3increases the compressive strength decreases. 0.50% MUSF giveshigher values of compressive strength than the cement pastescontaining higher dosages. Therefore, 0.50% MUSF is the optimumvalues of MUFS to be added as a water reducer and accelerator. Theincrease of the dosage up to 0.5% retarded the hydration at early ages(1-3 days), due to the retardation effect ofMUSF.7- The change in the electrical conductivity reflects the physico-chemicalchanges in the cement pastes and it can be used to monitor setting andhardening processes. Significant changes in electrical conductivityoccur when the paste gains its rigidity. On increasing the amount ofpolymeric materials, the conductivity maximum was found to haveshifted to longer hydration times.