Учебное пособие 2112

Fig. 5. Cement stone during slowing down of hydration, = 12 h. … 7 days

During slow interaction also associated with self-organizing structural forming after 7 days of hardening the gaps between the envelopes and surface of the grain are filled, peripherial areas of the cement grain are replaced with calcium silicate hydrogel and the reaction shifts to the centre of the grain (Fig. 6).

In the cement stone and in the rest of large and completely involved grains there are three areas C-S-H:

а) outside layer of about 1 mkm thick formed in the solution in the space originally filled with water;

b)an intermediate layer of about 8 mkm thick that is also precipitated using the solution on the inside layer of the envelope, i.e. the space taken up by the cement grain;

c)a central part formed topochemically.

As hydration and structure formation evolve, the structure of the porosity of the cement stone changes. As hydration progresses, the volume of capillary pores reduces and so does their radius and the total volume of gel pores increases. As a result of hardening the total porosity of the cement stone drops. As the radius of the pores decreases, there is less free water in the system respectively and liquid phase of the cement stone is now dominated by capillarly connected and absorption water.

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Therefore the original intergranular volume during hydration is filled by newly formed substances by 50…60 % in relation to the solid phase in the original “water –– cement” system. In the resulting structure of the cement stone the solid phase takes up 65…82 % depending on the water-cement ratio. The remaining grains of cement take up 12…23 % in the solid phase, hydrosilicate gel — 50…60 %, Са(ОН)2 — 20…25 %, calcium hydrosulphoaluminate — 15…20 %. The structure of the porosity is presented by capillary pores (20…30 % of the total volume of the pores), gel pores and crystal joints (70…80 %). The proportion of free water in the resulting structure of the cement stone is not over 1…2 % of the mass of the solid phase.

d ≈15 mkm

d > 60 mkm

Newly formed substances in the volume: outside fiber needleshaped CSH (C/S ≈ 2,6––2,7), ettringite crystals and alumoferrite phase l ≈ 2––10 nm, Ca OH

d ≈ 50––100 nm

Fig. 6. Cement stone during slow interaction, ≥ 7 days

2. Requirements for the structure of a cementing substance. In developing the technology of nano modification one must keep in mind the above qualitative and quantative changes of the structure of the cement stone at different stages of hydration and hardening. Nano effects should be produced by obtaining the structure of the cement stone meeting the requirements for the strength performance R . According to the general approaches to improving the failure resistance performance mentioned using nano modification of individual crystals, crystal joint (crystallite) and cementing substance mentioned in 6 and considering the characteristics of

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structural elements of a cementing substance, requirements for the structure of the cement stone in its different scope levels can be specified.

For individual crystals according to the requirements for improving the strength limit of a structural unit sized d, crystal chemical and morphological characteristics and number of defects are corresponded by the phases CSH(II), CSH(I), С3А·3СŜН32.

For crystal joint (crystallite) when the effect of individual crystals on its strength is implemented through a spatial and geometric construction of a joint, failure resistance performance can also be achieved by forming hydrosilicate phases of jelly-like and fiber needle-shaped morphology and АFt-phase as they provide as many as possible strong contacts in a volume unit.

For a cementing substance improving the failure resistance of a structure is associated with optimization of volumetric ratios of the components of the solid phase:

––hidden crystal (С5S6Нх5, CSH(I)) improving the viscocity of failure of the material due to plastic deformation capacity and thus providing extra energy costs to generate plastic deformations;

––fiber needle-shaped CSH(II), CSH improving the energy costs of the failure energy due to a lot of chaotic contacts and boundaries in the volume;

––plate prismatic (АFmand АFt-phases) for extra “self-microreinforcement” of a cementing substance.

Improving the strength characteristics is also achieved by increasing the volume of crystal and gel pores.

3. Factors of management and outcomes of nano modification during evolution. Summing the results of theoretical considerations of evolution of the structural formation of cement systems, factors of management can be identified and outcomes of nano modification at each stage are assumed.

At the stage of the generation stage (at the initial and pre-induction hardening stage) the

major factors of management are degree of oversaturation ( кр) of the original solution influencing the rate and parameters of the structure of an emerging crystal. Hence nanotechnology can make use of regulating oversaturation, e.g., by introducing into a system of nanoparticles with a similar crystal chemical structure to change emerging centres of crystallization (Ic) and (or) regulating the solubility by thermal or other effects on the system. As a result spontaneous dispersion of the cement system can be expected to accelerate as well as the structuring of hardening water followed by a reduction in Gibbs energy of the generation of the solid phase and molecular cluster of an emerging principal hydrate.

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At the stage of the growth of particles (induction period of hardening) such parameters of the system as the coefficient of a crystal shape, number of possible point defects in a volume unit of a crystal can be changed by and as a result of nano modification. Structure forming involvement and modifying effect of additives of nano modifiers at the growth stage and accumulation of particles are associated with a catalytic role of nano-sized particles as centres of crystallization with the corresponding effect of reducing an energy threshold of this process (Еact) and its acceleration (dV). It should be noted that the major factor of management at this stage is creating extra centres of crystallization and that can be done by introducing a specified dosage of nano-sized additives of an optimal size and appropriate crystal chemical structure.

Therefore due to the introduction of nano-sized additives at these stages there might be a shorter induction period, a reduction in the radius of emerging crystals of principal hydrates, which might boost ultra micro grain structure of a cementing substance thus having a lower degree of defects of individual crystals.

The driving force behind agglomeration (acceleration of hydration) is the system seeking to reduce the area of the boundary of phases (Sreduc), which causes changes in the number of particles making up an aggregate (Np) and the total area of the boundary of the phases ( S). As the original emerging particles become smaller during nano modification, there is more energy coming out (Еaggl), which promotes intensification of agglomeration and makes it shorter. These parameters can be considered major factors of management during nano modification at this stage. The outcome of nano modification will be the formation of a structured liquid phase, which is normally achieved by introducing plasticizers and superplasticizers as tools of nano modification. Structure forming involvement of plasticizing additives is due to mechanisms providing changes in thermal dynamics and kinetics of the process making it possible to regulate the size and shape of an agglomerate, joint, number of crystals and contacts in them. A combination of effects of nano additives and superplasticizers might predominantly cause hydrosilicate phases of fiber and needle shaped morphology as providing the most joint and growth contacts in a volume unit.

At the stage of self-organizing structural formation (slowing down and slow interaction), a cementing substance is modified as it is emerging, the same applies for a volumetric ratio of the crystal and amorphous phases, i.e. a volumetric ratio of morphological differences of hidden crystal, fiber and needle-shaped, plate and prismatic. It also changes a specific volume of crystal and gel pores.

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The following can be expected as the outcome of a modifying effect:

1)changes in the state of the intergranular surface of the system;

2)formation of extra types of the boundary area;

3)arranged structures of hardening with a dense envelope of crystals with corresponding changes in the porosity of a crystal joint.

At this stage the outcomes of nano technological modification from the previous stages will be mediated. E.g., this might apply for zoning of a hardening structure.

Conclusions

1. Systematization and analysis of major periods of inhomogeneous structural forming of cement systems (hydration hardening systems) provided insight into the generation of the phase, growth of particles, their agglomeration, spontaneous and self-organizing transformation in time as an object and objective of nanotechnological management.

2. A spatial and geometric setting of the transformation of the “cement –– water” system in all the traditional stages of hydration has been described both at the initial and induction period, acceleration, slowing down and slow interaction. As a result qualitative and quantative changes in the structure of the cement stone are presented as an object of nano modification which must be carried out on condition of obtaining a cement stone to meet the strength per-

formance criterion R .

3. Factors of directly nano modified structural elements of the system at the stage of the generation and growth of crystals have been justified and they are a combination of nano-sized additives of an optimal size and appropriate crystal chemical structure in combination with superplasticizers. Their use enables the regulation of the morphology of individual crystals, sizes and shapes of an agglomerate, joint, number of crystals and their contacts. It is also indicated that at subsequent stages of agglomeration and self-organizing structural formation of the structure of a cementing substance their effect is mediated and what it does is that it changes a volumetric ratio in its morphological differences, zoning and clustering of microstructure.

The authors extend their gratitude to the academician of the Russian Academy of Architecture and Building Sciences, PhD. in Technology, Prof. Ye. M. Chernyshov for his incredible contribution and consultancy.

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References

1.Artamonova, O. V. Koncepcii i osnovaniya texnologij nanomodificirovaniya struktur stroitel'nyx kompozitov. Ch. 1: obshhie problemy fundamental'nosti, osnovnye napravleniya issledovanij i razrabotok / O. V. Artamonova, E. M. Chernyshov // Stroitel'nye materialy. — 2013. — № 9. — S. 82—95.

2.Chernyshov, E. M. Avtoklavnoe sinteznoe tverdenie silikatnyx materialov: razvitie prostranstvennogeometricheskoj koncepcii strukturoobrazovaniya / E. M. Chernyshov, V. A. Popov // Dostizheniya stroitel'nogo materialovedeniya: sb. st. po materialam mezhdunar. nauch.-texn. konf. — SPb, 2004. — S. 32—39.

3.Pashhenko, A. A. Teoriya cementa / A. A. Pashhenko. — Kiev: Budivel'nik, 1991. — 168 s.

4.Granovskij, I. G. Strukturoobrazovanie v mineral'nyx vyazhushhix sistemax / I. G. Granovskij. — Kiev: Naukova dumka, 1984. — 300 s.

5.Vest, A. Ximiya tverdogo tela. Teoriya i prilozheniya: v 2-x ch.: per. s angl. / A. Vest. — M.: Mir, 1988. — Ch. 1: 558 s.; Ch. 2: 336 s.

6.Chernyshov, E. M. Koncepcii i osnovaniya texnologij nanomodificirovaniya struktur stroitel'nyx kompozitov. Ch. 2: K probleme konceptual'nyx modelej nanomodificirovaniya struktury / E. M. Chernyshov, O. V. Artamonova, G. S. Slavcheva // Stroitel'nye materialy. — 2014. — № 4. — S. 73—83.

7.Kashkarov, V. M. Khimicheskaya modifikatsiya poverkhnosti poristogo i profilirovannogo kremniya v rastvore akrilovoy kisloty / V.M. Kashkarov, A.S. Len'shin, P.V. Seredin, B.L. Agapov, V.N. Tsipenyuk // Poverkhnost'. Rentgenovskie, sinkhrotronnye i neytronnye issledovaniya. –– 2012. –– № 9. –– S. 80.

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TECHNOLOGY AND ORGANIZATION OF CONSTRUCTION

UDC 728.8

V. Ya. Mishhenko1, Ye. P. Gorbaneva2, Yoeun Rithy3, Fan Noot Lin4

APPLICATION OF THE FLOW METHOD OF CONSTRUCTION

OF URBAN LOW-RISE RESIDENTIAL DEVELOPMENT IN HOT CLIMATES

Voronezh State University of Architecture and Civil Engineering Russia, Voronezh, tel.: +7 (4732) 76-40-08, e-mail: oseun@yandex.ru 1D. Sc. in Engineering, Prof., Head of Dept. of Construction Organization, Assessment and Management of Real Estate

2PhD in Engineering, Assoc. Prof. of Dept. of Construction Organization,

Assessment and Management of Real Estate

Ho Chi Minh City University of Architecture Vietnam, Ho Chi Minh, e-mail: oseun@yandex.ru 3Prof.

Voronezh State University of Architecture and Civil Engineering Russia, Voronezh, tel.: (4732)76-40-08

4PhD student of Dept. of Construction Organization, Assessment and Management of Real Estate

Statement of the problem. The article is devoted to the planning of urban construction of low-rise residential development in climate and socio-geographical conditions of Cambodia.

Results. To search for rational organizational and technological solutions for the construction of lowrise residential projects a criteria is proposed that would ensure a minimum of time and finance for the construction. The paper also deals with modern trends of development of the typology of accommodation in Cambodia, the specific features of the construction in a tropical climate. Various methods of organizing construction and installation works, construction of diagrams of objects, as well as an algorithm for sequence development schedule line method, taking into account the organizational and technological relationship between the works and installations are considered.

Conclusions. The choice of rational variants of organizational and technological solutions of construction of low-rise residential buildings using the sequential algorithm development schedule line method, taking into account the criteria imposed makes planning and organizing of the construction of low-rise urban areas efficient.

Keywords: planning, construction, low-rise buildings, scheduling, methods of organization of work line method of work organization, organizational and technological parameters.

© Mischenko V. Ya., Gorbaneva Ye. P., Yoeun Rithy, Fan Noot Lin, 2016

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Introduction

Timely planning of low-rise construction is crucial for it to run smoothly and properly. The outcome of a construction firm’s job depends on how well-planned the work to be done is. Insufficient and untimely planning contributes to lower revenues through the entire construction planning. Therefore planning of low-rise urban construction considering modern trends in the housing of Cambodia needs to be addressed in order to identify the criteria for viable organizational and technologic solutions, to employ a range of methods of organizing construction and assembly as well as to design an algorithm for developing a calendar schedule by means of linear scheduling method.

1. Features of the construction of low-rise buildings in the climatic and geographical conditions of Cambodia. Modern tendencies in the housing architecture of Cambodia and abroad are intrinsically connected with social economic and political conditions. Particular housing standards are characteristic of each historic epoch. A housing standard are living conditions that are deemed standard at a particular point of time. A housing standard is stipulated by the housing legislation, construction standards and housing distribution, traditions, customs and public perceptions. Therefore processes in the housing construction are imperatives for social housing aspirations. Obviously, some people’s living conditions are insufficient. Therefore there is housing problem and policy to be addressed by the state.

Modern tendencies in the development of types of housing in Cambodia and abroad involve a shift from types of housing of the epoch of small-scale industry to that of large-scale industry. The following features of architectural organization of housing are crucial:

1)an increase in the number of high-rise buildings, a shift from lowto high-rise housing especially in cities;

2)location of residential buildings in vacant spaces inside the city and reconstruction area;

3)developed functional program of housing network including shared and private premises –– a guest’s room, dining room, study, toilet and bathroom in each living space, healthy block, etc., larger and better-equipped premises;

4)active role of the layout of apartments or houses played by open spaces such as terraces as well as terraces with pools, driveways, winter gardens, greenhouses, recreational areas, etc.;

5)designing areas for recreation, service and self-service depending on tenants’ demands;

6)combine planning structures dominating low-rise construction;

7)use of monolith concrete with different envelope structures of brick, small blocks of lightweight concrete as the major material for load-carrying structures.

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There is an emerging shift to minimum standards providing decent living conditions. In social organization of construction there is now a tendency for cooperations based on private homeownership and social ownership (condominium). A shift for construction firms designing, producing building materials and constructing housing holds a great promise for the construction industry.

Special features of low-rise construction are also that the customer (individual) has certain demands, i.e.:

––minimum costs for maintaining a living a space. Therefore it is necessary to seek out construction and technology solutions that are energy and (or) heat saving. Heat losses of enveloping structures must be not over those specified in the Building Guidelines and Regulations;

––the delivered quality of the work should be up or live up to that expected. This gave rise to the term “Western-style renovation”;

––construction cost must be kept to a minimum. This makes it necessary to search for technological and organizational solutions involving minimum material;

––construction of living spaces (especially not for sale) must be completed by the summertime (March-June), i.e. before the property market gets too busy.

These make it necessary to look for solutions to provide quality in compliance with the customer’s demands and wishes.

One of these is also choice of construction solutions for low-rise buildings where the outcome would be energy sustainable and the corresponding technology costand resource-effective. This is particularly important that due to a shift of housing priorities to low-rise buildings there is a growing demand and thus supply for different construction, material and technological solutions involved in their construction. Based on that there is a need for evaluating these supply in terms of materials as well as technology. This concerns those for enveloping structures (wall, roofs), partitions, floors, finishing, etc. Current priorities are wall options that accounts for 60% of the entire construction costs.

Another pressing issue is search for technologies and organization of low-rise buildings that would involve minimum time and to financially benefit for the customer and contractor, i.e. construction should cut down on prime costs and generate sufficient rent revenue.

2. Planning construction and assembly using linear scheduling method. For a rational search for technology and organization solutions for low-rise buildings to keep the time and cost to a minimum and financially benefit the customer and contractor (i.e. lower prime costs and higher rent revenues), it is necessary to address calculation and optimization of construction. Graph models as linear calendar graphs, cyclograms and net graphs are increasingly used in organizational and technological planning. These are planning documents where based on

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construction and assembly and adopted technologies and organizational solutions low-rise construction is specified in terms of sequence and time. The time is planned as a result of rationalizing the time of performing individual work based on the content, amount of major resources, primarily construction teams and leading mechanisms as well as specific conditions of construction areas, particular sites and other significant factors.

Any set of construction operations can be performed using different combinations of works in time and space as well as different economic and technological levels. Therefore dealing with all possible options of organizing a set of construction procedures to compare and select the most viable one for particular construction conditions is of tremendous interest.

The model of calendar planning is essential to its method. This organization method is central to the sequencing of work in time and space.

The organization methods are determined by:

––dynamics of intensity of construction procedures;

––degree of their combination in time;

––restrictions on the interaction of particular procedures in one area.

Constant and random intensity of works is the major classifier that breaks the organization down into three differently significant groups (Fig. 1). A degree of their combination is the main criterion that determines the overall method of organizing construction.

Fig. 1. Methods of organizing construction

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