Structure both properties цементного of the test and hardened cement (stone).

As a result of careful mixture цементного of a powder with water taken in quantity(amount) 25-40 % of his(its) weight, receive цементное тесто, named differently by paste. With increase of quantity(amount) of water тесто becomes more mobile, the consistence it(him) decreases.

1. Structural viscosity and plastic durability of the test.

Тесто, made from cement or from any of other knitting substance, represents concentrated water суспензию, described by the certain structure and, hence, by raised(increased) viscosity. Viscosity similar суспензий define(determine) under the formula:

 

? =? н +? стр,

 

Where? н - normal or ньютоновская viscosity of system;? стр- additional, structural viscosity of the same system. Such systems name вязкопластичными. Occurrence of the raised(increased) viscosity separate charge ван-дер-ваальсовых of forces, in this or that measure connecting высокодисперсные частички in суспензии. The destruction of such structures comes, in particular, at mechanical influences on system (vibration, pushes, встряхивание, hashing and т. Item). Thus the structural viscosity falls, and суспензия gets ability a leak. At the termination(discontinuance) of mechanical influences the structural communications(connections) in system again are restored, the viscosity суспензии raises, and the fluid condition disappears. The similar systems are called тиксотропными.

The normally viscous systems begin a leak at any difference of pressure. At the structured systems on Бингаму it is necessary to apply(put) additional force appropriate to a limiting pressure(voltage) of shift to call their current.

The structural viscosity to a great extent depends both on properties of cements, and from concentration, temperature and duration выдерживания суспензии. It is important to note, that depending on В/Ц and the durations выдерживания of the test considerably change character and time subsequent застудневания at the termination(discontinuance) of mechanical influences, together with structural viscosity. For definition of structural viscosity цементных of pastes and solutions And. Е. Десов has developed вибровискозиметр. In a fig. 17 the results of some definitions of structural viscosity of the test from usual cement, and also test with the additive пластификатора - омыленного пека in quantity(amount) 0,05 and 0,1 % of weight of cement are given. Пек, being by superficial - active substance (ПАВ), promotes significant reduction of viscosity цементного of the test, and also растворных and concrete mixes, best them удобоукладываемости, increase of density and, hence, their qualities.

At introduction in портландцемент трепела, диатомита, опоки and т. The item structural viscosity sharply grows. So, if to the test made at В/Д = 0,5 to add 30 % трепела, the structural viscosity is increased in tens time.

 

 

Fig. 17. Structural viscosity pure(clean) цементного of the test and with the additive омыленного пека

 

1 - портландцемент + 0,05 % пека;

2 - портландцемент pure(clean);

3 - портландцемент + 0,1 % пека

Physical and mechanical properties of cements

 

1. Density and volumetric weight.

Density портландцементов depending on chemical and phase structure, and also various additives changes within the limits of 3-3,2 г/см3.

The cements with lowered density at equal activity, водопотребности and speed твердения in comparison with cements with raised(increased) density are more economic, as at the identical weight charge knitting give more пластичные concrete mixes because of the increased output(exit) цементного of the test.

The cements with raised(increased) density are used at erection of accident protection devices from nuclear radiations. They are applied also at цементационных jobs and for тампонирования of petroleum chinks. Such cements with raised(increased) density receive at the expense of increase in their structure of ferruterous phases С4АF and С2F. In necessary cases in structure of cements at their manufacturing enter окись бария ВаО, which reacts with кремнеземом with education 2ВаО ·SiO2 (density 5,4 г/см3).

Slag and пуццолановые портландцементs are characterized in lower density (2,7-2,9 г/см3), than usual портландцемент.

So-called bulk volumetric weight of cement is connected also to density. Distinguish volumetric weight (weight) in the friable and condensed condition. Than less than density and than is more thin the cement is crushed, the his(its) volumetric weight is less. Bulk volumetric weight портландцемента in a friable condition changes within the limits of 900-1100, and in condensed - 1400-1700 kg / м3.

To know volumetric bulk weight of cement it is necessary at account of volume of bunkers and силосов for his(its) storage, at volumetric дозировании making of concrete and т. Item. Often in accounts of volume of warehouse capacities accept average bulk weight of cement in 1200 kg / м3.

 

2. Водопотребность and normal density of the test.

Under водопотребностью of knitting substance understand that quantity(amount) of water, which is necessary for entering into him(it) for reception of the test with so-called normal density. As normal density цементного of the test such consistence conditionally is called, at which пестик Тетмайера is immersed in him(it) on certain(determined), normalized by the standard 310-60, depth.

Водопотребность of cement at reception of the test of normal density is equal to quantity(amount) of water designed in percentage of weight of cement. Водопотребность портландцементов changes usually within the limits of 24-28 %. It is necessary to note, what is it sometimes it is more necessary for passage of reactions гидратации клинкерных of minerals. In result entered in тесто superfluous water raises пористость цементного of a stone, that negatively has an effect for his(its) durability. Therefore ври other equal conditions, than less водопотребность of knitting substance, the higher is his(its) quality. Портландцемент concerns to knitting substances with lowest водопотребностью. Водопотребность of building plaster, for example, 50-70 %, and пуццоланового портландцемента - 35-40 % (reaches(achieves) at the additives осадочного of an origin).

Водопотребность портландцемента depends on many factors and, in particular, from it(him) минералогического of structure. The it is more in him алюминатов кальция, the she is higher. More thin crushing also increases her(it) a little. This is promoted also by introduction of such materials, as трепел, диатомит and other active additives осадочного of an origin, even in quantity(amount) 10-15 %.

Водопотребность of cements it is possible to adjust in significant limits with the help of the additives of superficial - active substances (ПАВ). They render разжижающее action. In quality ПАВ apply сульфитно-спиртовую барду and its(her) derivative, абиетат натрия and many other materials more often. ПАВ in quantity(amount) 0,1-0,3 % enter in cements at помоле, and receive so-called пластифицированные портландцементы. They can be added and at manufacturing растворных and concrete mixes.

 

3. Схватывание of the test.

The large practical meaning(importance) at use of knitting substances gets speed them схватывания and твердения.

Схватыванием the process is called, at which the rather mobile mix of cement with water gradually густеет and gets such initial durability, at which its(her) mechanical processing becomes practically inconvenient and even impossible (in the end схватывания). Therefore knitting substances, including the cements, should be characterized by such terms схватывания, which allow приготовлять растворные and concrete mixes and to use them in business.

Distinguish a beginning and end схватывания of the test from this or that knitting. Conditionally according to the standards these terms схватывания define(determine) on the test of normal density at temperature 20ЁС + 2 on depth of immersing in him(it) needles Вика. On ГОСТу on портландцемент the beginning схватывания of the test from this knitting should come not earlier than 45 mines, and end схватывания - not later than 12 ч, considering from the moment of mixture of cement with water.

Knitting of themes ценнее, than faster his(its) durability the ambassador of a beginning схватывания and, hence, than less break in time between his(its) beginning and end accrues. Terms схватывания of cements depend on many factors and submit to regulation in rather wide limits in view of the requirements showed to knitting, used in construction.

Минералогический the structure of cements is appreciably reflected in speed them схватывания. So, the cements with the raised(increased) contents алюминатов кальция are characterized by shorter terms схватывания. Белитовые cements are seized more slowly.

Terms схватывания of cements are influenced also by(with) many other substances, one extend them, others reduce.

 

4. Uniformity of change of volume

The knitting substances, including cements, at твердении should be characterized by uniformity of change of volume. The cements with non-uniform change of volume result not only in decrease(reduction) of durability of concrete at them твердении, but even to their destruction.

The non-uniformity of change of volume of cements can be called:

1) гидратацией free окиси кальция at the contents her(it) in клинкере more than 1,5-2 %;

2) гидратацией free окиси магния, present in клинкере as high-temperature slowly гасящейся of the form - периклаза;

3) Education in hardening cement высокосульфатной of the form гидросульфоалюмината кальция at the raised(increased) contents in клинкере С3А and at superfluous introduction of plaster in портландцемент at it(him) помоле.

 

5. Activity both durability портландцементов and their dependence on the various factors.

а) Definition of durability and stamp of cements under the standards

Major property портландцемента is his(its) ability to harden at interaction with water and to pass in камневидное a condition.

Than the above mechanical durability hardened камневидного of a body (solution, concrete) and than faster she is achieved, the higher is the quality of cement or other knitting substance. Therefore distinguish:

1) Final durability, which can be achieved by cement at твердении, and

2) Speed твердения, characterized by intensity of growth of durability of hardening cement in time.

 

6. Influence of temperature and additives on speed твердения портландцементов.

Temperature renders the very large influence on твердение портландцементов and his(its) derivative (slag and пуццоланового портландцемента etc.)

7. Усадка and набухание цементного of a stone at change of his(its) humidity.

If previously sample, sated with water, of this or that form (prism, cylinder and т.п.0, made from цементного of the test, solution or concrete to place on air environment(Wednesday), which relative humidity below achievable at complete saturation, the sample will begin to dry up thus water in the beginning to evaporate from large cavities and пор, and then from capillaries of the lesser diameter. She will evaporate until, when the balance between moisture content in a sample and in an environment (relative humidity) will be established.

8. Variable humidifying and drying цементного of a stone.

 

If the cycles of drying and humidifying цементного of a stone or concrete repeatedly repeat, being accompanied by processes, varying on a direction, усадки and набухания, residual deformations gradually collect, the structure is loosened, external volume and пористость of system is increased, and mechanical durability and durability of concrete (are reduced.

 

9. Трещиностойкость

 

Усадка цементного of a stone and цементных of concrete is closely connected from them трещиностойкостью during drying, which has the large practical meaning(importance). For example, at evaporation of water from a surface цементного or concrete sample more intensive develop усадочные of deformation, him in internal zones of a material, where влагоотдача or is slowed down, or her(it) completely no. Because of it in internal zones there are pressure(voltage) of compression, and in outside layers - stretching.

The researches show also, that the cements with approximately identical parameters усадки can considerably differ on трещиностойкости. Believe, that the cements with the lowered speed твердения are characterized by smaller propensity to трещинообразованию. Therefore to judge about трещиностойкости of this or that cement only on parameters it(him) усадки it is impossible.

 

10. Ползучесть цементного of a stone

Ползучестью the property цементного of a stone is called or concrete is irreversible to be deformed under influence is long of pressure,(voltage,) working in them arising at action of external loadings, and also усадки, temperature and other factors.

Depending on size of the enclosed forces the deformation ползучести or is gradually stabilized at some constant level, or, being continuously increased, results in destruction of a body.

At pressure(voltage) in concrete till 50-60 Ё/о of a limit of his(its) durability at compression ползучесть carries linear character and is caused mainly by viscous current of a material at малозаметном infringement of his(its) microstructure.

 

Questions

1. What such viscosity?

2. What concerns to физико-mechanical properties of cements?

3. Characterize each property of cements.

 

 

Тиксотропия –thixotropy

Самопрoизвольно – themselvs liberally

Водопотребность –water demand

Тесто – dough, paste

Кварц – quartz

Полевой шпат – Feldspar

Стекло – glass

Базальт –basalts

Доменный шлак –furnace slag

Отношение О : Si – relation, attitude toward

Кристаллизации – crystallization

Oксид кальция – calcium oxide

Магния – magnesium

Марганец - manganese