Functionality of mortar and concrete mixes is regulated by surfactants, which act as plasticizers. The molecular structure of these admixtures can be changed during hydration of alkali-activated cements (AAC). The objective was to determine the chemical nature of plasticizers effective for property modification of mortars and concretes based on AACs with changing content of granulated blast furnace slag from 0 to 100 %. The admixtures without ester links become more effective than polyesters when content of alkaline component increase. The admixtures effective in high alkaline medium were used in dry mixes for anchoring (consistency of mortar 150 mm by Vicat cone; 1 d tensile strength in bending / compressive strength of mortar 6.6 /30.6 MPa) and in ready-mixed concretes (consistency class changed from S1 to S3, S4 with consistency safety during 60 min; 3 d compressive strength of modified concrete was not less than the reference one without admixtures).
Проаналiзовано сутнiсть проблеми власних деформацiй лужних цементiв (ЛЦ), ускладнення якої пов'язано з пiдвищеним вмiстом гелеподiбних гiдратних новоутворень. Як приклади розглянуто типи цементiв дiаметрально протилежнi за композицiйною будовою i вiдповiдно за вмiстом гелеподiбних фаз при гiдратацiї-лужний портландцемент (ЛПЦ) i шлаколужний цемент (ШЛЦ). Запропоновано пiдходи до формування ефективної структури штучного каменя, протидiючою деформацiям усадки, шляхом втручання в структуроутворення при використаннi комплексiв мiнеральних i органiчних сполук. Такi сполуки в складi комплексних органо-мiнеральних добавок сумiсно впливають на iнтенсифiкацiю кристалiзацiйних процесiв, формування ефективної порової структури та морфологiю гiдратних фаз при зменшеннi вмiсту води в штучному каменi. В якостi iнгредiєнтiв запропонованих комплексних добавок-модифiкаторiв розглянуто солi-електролiти рiзного анiонного типу та анiоноактивнi поверхнево-активнi речовини. Виявлено, що для модифiкацiї ЛПЦ найбiльш ефективною є система «сiль-електролiт-поверхнево-активна речовина». Показано, що модифiкацiя ЛПЦ комплексною добавкою цiєї системи на основi NaNO 3 забезпечує зменшення усадки з 0,406 до 0,017 мм/м. Натомiсть використання Na 2 SO 4 забезпечує цьому типу лужного цементу здатнiсть до розширення в межах 0,062 мм/м. Показано, що ефект компенсованої усадки модифiкованого ЛПЦ пов'язаний з бiльшою кристалiзацiєю низькоосновних гiдросилiкатiв (CSH(В)) i гiдроалюмiнатiв кальцiю (CaO•Al 2 O 3 •10H 2 O). Додатковий ефект пов'язаний з утворенням сульфатвмiщуючого натрiєво-кальцiєвого гiдроалюмiнату (для системи на основi Na 2 SO 4) та кристалiчного гiдронiтроалюмiнату кальцiю (для системи на основi NaNO 3) з вiдповiдним напруженням мiкроструктури. В розвиток для модифiкацiї ШЛЦ запропоновано комплексну добавку системи «портландцементний клiнкер-сiль-електролiт-поверхнево-активна речовина», яка забезпечує зменшення усадки з 0,984 мм/м до 0,683 мм/м. Мiнiмiзацiя усадки модифiкованого ШЛЦ пояснено формуванням поряд з низькоосновними гiдросилiкатами кальцiю гiдроалюмосилiкату натрiю типу гмелiнiту ((Na 2 Сa)•Al 2 •Si 4 •O 12 •6H 2 O) з пiдвищеним ступенем закристалiзованостi. При цьому вiдмiчено, що структура цементного каменя характеризується пiдвищеною щiльнiстю, однорiднiстю i монолiтнiстю гiдратних новоутворень Ключовi слова: лужний цемент, сiль-електролiт, комплексна органо-мiнеральна добавка, структуроутворення, власнi деформацiї, усадка
Optimization of complex shrinkage-reducing additives (further, SRA’s), consisting of ordinary portland cement clinker (further, OPC clinker), salt-electrolyte and surfactants, is provided for prevention of steel reinforcement corrosion due to shrinkage mitigation in alkali-activated slag cement (further, AASC) fine concrete. Modification of AASC by SRA included 0.3 % sodium lignosulphonate, 0.15 % sodium gluconate, 1.4 – 2.0 % NaNO3 and 6.5 - 7.7 % OPC clinker (by mass of granulated blast furnace slag) provides shrinkage reduction from 0.984 up to 0.560 – 0.605 mm/m (t=202 °С, R.H.=65 %). Unlike, SRA presented by the mentioned system with 1.50 - 1.59 % Na2SO4 and 4.0 - 4.65 % OPC clinker causes shrinkage mitigation from down to 0.625 - 0.640 mm/m. In addition, SRA with 1.80 - 2.05 % Na3PO4 and 4.0 - 4.6 % OPC clinker minimizes shrinkage to 0.713 - 0.700 mm/m. Shrinkage mitigation in modified AASC fine concrete is explained by less water, higher crystallinity of hydrated phases as well as by formation of minamiit (Na,Ca0.5)Al3(SO4)2(OH)6, calcium hydronitroaluminate ЗСаО∙А12О3∙Са (NO3)2∙10Н2О and calcium hydroxylapatite Са10(РО4)6(ОН)2 crystals versus salt-electrolyte, i.e. Na2SO4, NaNO3 and Na3PO4 agreeably. The 28 day compressive strength of modified AASC fine concrete is not less than the reference one (48.0 - 56.0 МPа).
In the article the effect of fillers of various chemical nature on the corrosion resistance of polyester powder coatings in terms of flaking widths and corrosion expansion widths in accordance with DSTU ISO 4628-8: 2012 was reviewed. According to the results of studies, the effectiveness of the use of fillers to increase the corrosion resistance of the powder coating varies depending on the average particle size and crystalline form of the filler was found. As a rule, in order to receive a powder coating based decorative coating you should apply only one layer of paint, while liquid coatings require applying several layers; this increases the time of coating production. The powder coating can be easily utilized and recycled, thus the economic feasibility of production increases.
Besides the fact that concrete recycling allows to avoid landfills disposal and contributes to a closed-cycle economy, such option may be very much in demand in war struck regions such as Ukraine, which after the end of the war, are faced with the problem of rebuilding and reconstructing. Beyond this emergency, even in peacetime extensive parts of the building stock will sooner or later need to be replaced and concrete recycling is called to play an increasing role there. However, depending on the technology and degree to which aggregates are recycled, concrete may be characterized by poor workability, reduced mechanical properties, increased shrinkage and reduced durability. This deterioration in the properties of recycled concrete is usually attributed to the characteristics of the old cement mortar remaining on the surface of the recycled aggregates, which is best considered as an additional volume of hardened cement paste with fine aggregate and additional porosity. This article attempts to underline how such key concepts help frame the current state of knowledge about concrete recycling, understand the implications of existing regulations, in order to define pragmatic and efficient routes for broadening the use of concrete recycling in war struck regions, with specific examples regarding Ukraine.
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