CC BY
9
И УДК666.972.16 (088.8)
¡1 EFFECTIVE ANTIFREEZING AGENT FOR ;:f CONCRETE MIXES
Sh.K. Torpichshev, F.Sh. Torpichshev
Pavlodar State University named after S. Toraighyrov
||f| Мацалада диметилдиоксанды вцдеудщ крсымша вншт, сондай-щ
|i||| диметилдиоксанды ректификациялаудан триметилкарбиналды фракцияныц кубтьщ цалдьщтарын а;ыщы бетондауушт эффектий суыща |||1 щрсы крсынды ретшде хрлданудыц зерттеулгр нэтижеЫ бершен. Бетонды §Щ крспага крсымша крсу-37о Стемпературага дейт бетонмъщтыпыгынын lllil unmeHcuemi цабылдануын цсштамасыз emedi.
ЩЦ В работе представлены результаты исследований по
|||i использованию в качестве эффективной противоморозной добавки для 1111 зимнего бетонирования - побочного продукта производства диметилдиоксана, в частности, триметилкарбинольной фракции кубовых остатков oms ректификации диметилдиоксана. Введение добавки в бетонную смесь обеспечивает интенсивный набор прочности бетона при температуре до -37о С
The work represents main test data on using antifreeze concrete admixtures as the effective agent for winter concreting. The antifreeze agent is a byproduct of dimethil-dioxane particularly trimethylcarbinol fraction of cubic residues resulted by dimethyl dioxane rectificatio.The admixture incorporation guarantees intensive concrete strength development up to - 370C.
In recent years the development of construction industry had revealed a great tempo thus stimulating the elaboration of fundamentally new technologies for performing concrete works under low temperatures. It is known that concrete hardening is accompanied by the span of utterly complex phenomena yet being not enough investigated and being of no full-scale control via various forces. This is due to diversity of active components of initial binding agent, by the complex system of new formations being synthesized and material itself being multicomponential etc.
The procedures of hydration are temperature-dependent, being intensive when it is on the rise, and declining when low, thus the temperature factor is to produce one of the strongest impact on the hardening of mineral binding agents.
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It is known that the temperature reduction up to OoC slows down concrete hardening dramatically. One can mention this precisely at early-ages of strength development for the speed of water-cement minerals reaction declines. But concrete structure cross-linking is affected differently by the temperature reduction i.e. the concrete of more solid structure is resulted by temperature compression of its constituents and more overall sedimentation takes it place.
What has been experimentally proved is that cement hydration and cross-linking under low temperatures are determined by the availability of the liquid phase which partial or total freezing evokes the hydration to slow down utterly or terminate totally. In heavy concretes containing no frost-resistant agents the prevailing water amount transfers into ice under -5oC (for high-branded cements this temperature is lower respectively). Since porosity and specific surface area tend to alter through the course of time the freezing point occurs to be non-constant and determined by these very factors.
Concerning the tests being done the prevailing ice span is obtained at temperature pulldown up to -5oC, when the ice content amounts 78% for heavy concrete cured for 24 h at normal conditions and 94% for frozen-at-once-after-preparation concretes.
In case the concrete strength by the moment of freezing is 50 or 70 % of R28 the amount of non-frozen water increases dramatically i.e. the concrete ice content is strongly affected by the hardening period before the start of freezing process.
Water undergoes supercooling and change of ice volume at various low temperatures in course of cooling and heat release, when ice gets crystallized.
Concrete structure undergoes modifications due to ice [being] concentrated in concrete and volumizing of frozen water in 9%, as well as growth of ice lens and ice crystals. The increase of pre-freezing curing period for concrete declines its expansion, less distorting its structure i.e. these procedures are affected by the early-strength of concrete.
Water-soluble chemical agents reduce the freezing point of concrete liquid phase, affect the solubility of binding agent and its hydration products, provide the hydration up to -20 oC due to systematic ice thawing. When introducing the addings their category of temperature range is of great importance i.e. the purpose of utterly low concrete hardening temperatures and availability to use these very agents as strength-developers and antifeezers. As well as ordinary concretes the hardening of the incorporated ones is affected by the moment of freezing. For instance when potash or sodium-potash incorporating concrete is frozen soon after manufacturing it reveals 30% of project strength loss and the degree of concrete structural failure is mainly determined by water amount and type of cement being used
Authors did draw very encouraging results when using the admixture - a by-produc of dimethyldioxane production, especially trimethyl carbinol fraction of cubic residues resulted by dimethyldioxane rectification.
The product of dimethyl dioxane manufacturing has the following chemical analysis, in mass.%:
Concerning the impact made on cement paste the mentioned admixture contains components of following properties:
" non-interacting with cement minerals, but increasing their solubility and declining the rate of water freezing point;
" activating the hydration of binding agent via dispersion of its granules, liquid phase destruction as well as increase of its solubility and declining water freezing point;
" intensifying the hydration due to exchange reactions which lead to Ca(OH)2 gels generation and also declining water freezing point;
" stipulating the calorification during hydration and declining water freezing point. At dissolution of trimethylcarbinol fraction of cubic residues resulted by dimethyldioxane rectification, occurs the chemical interaction of its [the fraction's] particles with water molecules resulting solvate coverings due to which the freezing point of water in pores decreases dramatically. Since the admixture's components remain long unbound in the porous liquid, they increase the ionic power of the solution that is to intensify hydration processes and as a result hardening of silicate cement phases. The aforesaid data is proved to be true via results of tests on special calorification of compos [=cement-sand solutions] and concrete contraction having an admixture presented. First N24h of hardening reveal that the admixture almost doubles specific calorification [=heat generation].
Due to growth kinetics research of incorporated compos' flexural strength it appeared that in all cases kinematics has a breakdown time which is followed by intensive
• trimethylcarbinol/tret-buthyl alcohol
• 4.4-dimethyl dioxane-1.3
• unsaturated spirits (mainly allyl one)
• methanol
• 2-methyl-3.4-dihydropyran 0 non-identifying compounds
73.25
7,20 2,44 3,74 0,17 0.22
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159
cross-linking. The increase of admixture concentration makes breakdown time shorten. The findings on growth kinetics of flexure strength do coincide with test data on the level of hydration via numerical x-ray and baking methods.
A concrete mix was prepared as following: pre-dozed dry mixes (cement/ fillers) were mixed in concrete mixer, after which a mixing water containing calculated amount of agent was added. The mix was stirred for 3-4 min and than casted in form.
Concrete compositions incorporating suggested agent (with breaking and optimal ingredients ratios), as well as reference and control concretes compositions (agents-off) are presented in Table 1.
Table 1.
Components Control composi tion Referen ce composi tion Suggested compositions
1 2 3 4 5
Cement 18,99 18,99 13,43 18,99 18,99 18,99 23,10
Sand 21,97 21,97 25,20 21,97 21,97 21,97 22,28
Macadam 51,65 51,88 54,70 51,15 51,88 50,85 44,73
AGENT 1 - 0,19 - - - - -
AGENT2 - - 1,21 1,71 0,19 2,56 2,08
Water OTHERS
AGENT 1 -an emulsion of mineral oils
AGENT 2 - tirmethylcarbinol fraction of cubic residues resulted by dimethyldioxane rectification.
Concrete mixes hardening was carried out without thermomoist treatment at +20o C, OoC and at -5, -24, -37 oC in multicellular freezing unit. Soon after forming samples were put to freezing room, than stroke at 48 h and left for further hardening for 26 days. At 28 day of room temperature hardening-thawing, at least for 12 h, the samples (with others gotten hardened at 20 o C, Oo C) were undergone tests on compressive strength and water resistance. Obtained results are presented in Table 2.
Table 2.
Numbers of Concrete mixes Decline of w/c ratio Compressive strength
compositions hardening in equally at
temperature constituent mixes, % 28 days
Control +20 - 100
0 62
-5 > 5
Prototype +20 3,4 11
(reference)
0 64
-5 12
Sugge 1 +20 13,6 132
sted
compo
sitions
-24 58
2 +20 13,6 130
-24 56
3 +20 5,7 113
0 73
-5 28
4 +20 17,0 134
-37> 47
5 +20 13,6 136
-24 56
As one can see the results listed in table 2 the reference concrete mix (prototype) can not provide the specified grade concrete strength when it hardens at temperatures lower than Oo C. If a concrete mix incorporates trimethylcarbinol fraction of cubic residues resulted by dimethyldioxane the hardening occurs to be intensive even at -37oC.
