THE EFFECT OF CEMENT COMPOSITION ON THE CRACKING RESISTENCE

G.DALAKISHVILI
(Georgia)

The resulte of studies of the cracking resistance of a hardened cement-sand solution prepared of 6 different kinds of cement are presented. Cracking is studied using the method of holography interferometry which enables to detect cracks at earlier stages than it van be done with other methods. Devices used to evaluate the cracking resistance in case of a combined action of shrinkage and mechanical load are described. The laboratory conditions for testing concrete are shown to be close to those in a real structure. Assuming the time elapaing from the befinning of observation of specimen to the moment of detection of a crack, as a measure of the cracking resistance, cements of different mineral compositions and different contents of unbaked components are compared.

The authors suggest to apply the method of holography interferometry to evaluate the ultimate extensibility of cement stone and concrete.




THE ENERGY DISSIPATION "NEGATIVE" HYSTERESIS EFFECT IN THE MODIFIED HEAVY AND LIGHT-WEIGHT CONCRETES UNDER THE CYCLIC LOADING

V.LOLADZE
(Georgia)

The work deals with the conditions of the "negative" hysteresis loop display in the melted sulphur impregnated concretes as well as in the finegrain and latex added light-weight concretes.

It is noted that in the concretes mentioned above the aggregate or the zone in the form of internal nucleus is in the compressed state.

It is concluded that the "negative" hysteresis effect in the concretes under cyclic loading results from the breaking of the structural connections in the part of the material which compresses the aggregate or the nucleus of the concrete.




PHYSICOCHEMICAL MECHANICS OF DEFORMATION OF CONSTRUCTIONAL MATERIALS IN SURFACE-ACTIVE MEDIUMS

M.LORDKIPANIDZE
(Georgia)

The purpose of the research is a detailed study of features of kinetics of development the deformation of constructional materials (concrete and steel in the first place), placed in the medium of substances, which are surface-active with respect to the given material (substance). This kind of study is necessary for further detailed development of the proposals (on the stage of applied research), intended for growth of performance characteristics of these materials.

We have found out new phenomena of this category, which consists in the following, that most of the solid bodies, placed in external medium, and having surface-active features with respect to its substance, have characteristic in development of deformation under external stress: - stage of nonlinear reversible deformations. During reaching this stage, the sizes of deformable object continue changing with the lapse of time, under constant, appurtenant external stress. This nonlinear deformation stops, when it reaches some limiting value. If the surface-active features are removed, and an action of external stress is kept, than the deformation will be returned to the value, expected in case of elastic deformation in absence of surface-active features. In case of removal of stress, the sizes of object returns to datum value, like in case of linear elastic deformation. The body in the medium of SAW (surface acoustic wave) can be undergone by such nonlinear reversible deformation iteratively, which each time returns to the ingoing size.

Such research will give a possibility to reveal for each material the proposed dependence of parameters of function, describing time dependence of nonlinear reversible deformation from external characteristics of deformable bodies (for example their sizes, condition of surface etc) and physicochemical parameters of their onteraction with the medium.

USE  OF  18ФТ  STEEL  FOR  PRODUCTION OF  A400C  (A500C) STEEL  REINFORCEMENT  AT  LTD.  “RUSTAVI  STEEL”

V.KOPALEISHVILI, N.MUMLADZE,  T.LOLADZE
(Georgia)

It  was  reported [1, 2] that production  of   reinforcing steel A500 C  using  high-temperature  thermo-mechanical  treatment (HTTMT)  is  complicated at  Ltd. “Rustavi  Steel”.  

Industrial  experiments  are  carried  out  on  18ФТ  steel  developed  by  us  and  positive  results  are  received according to which the  finished  product meets the  A400 C  steel  reinforcement  requirements.  Required mechanical properties (σ y ≥ 400 N / mm2)  are  obtained  in  hot -rolled  state  without heat treatment.  It  allows  to  solve  problems  while  rolling   large  diameter  ( N 25, 28, 32  mm )  steel  reinforcement. The  same  composition  will  promote  the use  of  relatively  safer  modes when  leveling  properties  along the full-length of the finished product  while  producing  A500C,  enabling to  combine 8-12 t melting  into  60-100 ton lots  according  to  their chemical composition, followed by industry regulation, along with the substantial economic effect.

At  the  second  stage   uniform,  weldable  steel  reinforcement  will  be  produced  without  heat  treatment -   in  hot-rolled  state→ B500 W,  with  the  yield  strength σ y ≥ 500N / mm2  according  to ISO 9655/2  standard. For  this  purpose  experiments will be  carried  out  on  steels  developed by us  (e.g. 13Г1С1ДФТ).  The advantage will  be  given  to  the most  corrosion  resistant  steel  in  ordinary concrete. Besides,  the  new phenomenon  considerably  simplifies  solution  of  the  problem.  

According  to  the  large-scale experimental data  and  the  result  analysis  it  is  proved that the reinforcing steel durability should be taken into account in  assessing  the  total specific destruction energy   (J/cm2),  because the higher  the   ,  the  longer  the  durability - resistance.