Panels and Cast-in-Place
April 14, 2015
Communism never came... When Nikita Khruschev signed "Elimination of excessiveness in design and construction" act in 1955 that marked the beginning of small apartment era, he really did a great thing. The country that had just started to recover from the post-war ruins, a substantial part of the population living in bunk houses, got a chance to live a decent life at last.
Initially it was planned that the residential initiative would be a transitional phase to the communist future that was expected to come after 20-30 years. That's why 5- and 9-storeyed houses had no "inexcusably increased hallways, corridors, and other auxiliary rooms"... Sixty years passed since then, communism never came, but those 'panels' still constitute just about the main type of housing in Russia (for example, in Moscow only there are over 40% of them, while in St.Petersburg they amount over 50% of all housing), though other construction technologies have long been around. What is the reason for such popularity and is this situation going to change in future?
At its time, panel housing was revolutionary for the construction industry, because it rally solved the housing shortage problem in the fast townifying world. For example, in the USSR starting from 1960s this technology allowed to commission over 110 million (!) square meters of housing per year. Similar pace was observed in Germany and France. What made such a rate possible was an industrial, actually conveyor approach. Parts are cast on a production line basis under generic designs, then transported to the site where they are assembled like tinker toys. If production technology is followed, such a panel house's life may be up to 50 years. Aside from a high building rate and simplicity, panel housing in Russia has some Soviet legacy in its support: a developed infrastructure of over 200 integrated house-building factories all over the country producing reinforced concrete parts. Accordingly, the construction cost of a panel building due to its availability and speed is relatively low (compared, for instance to cast-in-place or brick construction). Eventually, the combination of cost and rate makes panel construction the leader in the state initiatives for social housing. According to specialists from Resheniye consulting company, up to 70% houses build on public funds are panel ones.
The disadvantages of panel buildings are well-known and they, in a sort of way flow organically out of their advantages. For example, mass production makes open plan practically impossible (it is determined by panel spacing). A high assembly speed yields a high reject rate primarily in the interpanel joints. Moreover, traditional panel houses have poor heating performance due to the poor above mentioned joints. With all this in mind, we can still position the panel houses but in the economy segment, which explains the fact that their share in today's Russian construction is not really big, about 20-25% (after cast-in-place and brick construction). However, we should admit that the poor quality problem is currently almost solved thanks to development of integrated seamless technology. Among the latter, needle gunning could be mentioned as an example: a concreting technology with the mix is applied layer by layer onto the surface under concreting by compressed air, using torcrete cement gun or concrete injection unit, and a compressor. In fact, this technology has been around for several decades, but in Russia it was introduced just 10 years ago (adopted by Russkaya Stena company). Besides, purely panel houses are gradually receding to the past as today mixed methods spread that combine, let's say, cast-in-place floors, and concrete panel fencing with subsequent joint sealing.
Cast-in-place technology that came to Russia quite recently, allows building free layout buildings with high strength and rigidity. By the way, cast-in-place has no interpanel joints that require additional effort to insulate. Such structures are durable (with a life cycle of over 150 years) and have excellent thermal and soundproof performance. Actually, the cast-in-place construction advantages come from the method itself: the load bearing structures and floors are made right in place of solid concrete, and the enclosure structures may be made of other materials (for example, brick). So this approach allows to put up buildings with virtually any configuration, with big spans, and unpartitioned inner space, which is especially valuable for modern people.
This feature makes cast-in-place practically the only method for in-fill development and construction in tight space (e.g. in historic quarters). Naturally, cast-in-place technology doesn't assume any joints, so no effort is required to seal them and then to keep them sealed. It also should be stressed that cast-in-place method's unique advantage is practically unlimited number of floor: Today the majority of buildings are made using this technology. And the prestressing technology and new development of new low-temperature types of concrete such construction has become all-year-round and no longer requires to stop for the cold period.
Cheap or Expensive?
Like the 'panels', advantages here have their respective disadvantages: unique designs result in higher labor costs, cast-in-place reliability and insulation performance require more material consumption. However, the opinions that cast-in-place costs next larger are hardly objective: as a rule, the existing price difference between buildings comes from the location rather than the construction method. This is confirmed by figures: according to Azbuka Zhiliya (Housing ABC), the average weighted supply price on the new homes market in 'old Moscow' (without elite housing), at the end of 2014 amounted to: 206.1 thousand rubles per square meter in cast-in-place houses, and 125.2 thousand rubles in panel ones. In 'New Moscow' one cast-in-place square meter costs 91.1 thousand rubles, and 88.5 thousand rubles in panel. The Greater Moscow area prices per square meter amounted to 74 and 70.3 thousand rubles respectively. It is obvious that as far as the land is cheaper, the price difference levels up to amount just 5%.
Meet the deadline
The only pronounced disadvantage of cast-in-place method compared with panel is construction period, where the latter has a clear lead. However, even this is not too significant, because technology is developing very quickly. As a specific example of a cast-in-place building's construction period practically match the one of the panel, Hyatt Regency Sochi in Sochi hotel can be mentioned. Using a special removable formwork system, the building's 20 storeys were put up in 5, which is quite comparable to the installation of an economy class high-riser. "Using the repropping stands between tables," says Dmitry Kobylin, deputy chief engineer at PERI, modern formwork system specialist company, "we can remove the modules and partially strip the floor as early as after just a few days, taking the table to the upper level. Two such sets provide a rate of 4 floors per month, but it is still possible to increase it up to 6 floors per month." Formwork tables in the hotel construction were used at the floors of two storeys simultaneously. In the formwork, 21mm thick special cast-in-place high-quality SVEZA film faced birch plywood was used. According to Alexander Atapin, South Federal District project manager at PERI, "Plywood as part of those systems has passed through all the floors, then the customer took it away to use on other projects. In formwork tables, plywood goes through more cycles, for it is fixed firmly with screws to the table boarding, its edges are painted, and during the mounting/dismounting the panels are hardly exposed to any mechanical damage."
Both are better!
Construction technology competition is quite a senseless thing in this case. Today, the differences between them are leveled out, each method is enriched by the other, which allows to provide better results for the customer. An not to get lost in the current environment, one should review Table 2 that professional realtors use. If we consider the data carefully and objectively, we'll see that today the differences between the panel and the cast-in-place method are chiefly aesthetical. In other words, it is about panels' standard layouts and facades versus cast-in-place's 'freedom'. Of course, one can argue about the calculated lifetimes: even the Soviet panel made under outdated technology, often shoddily, have stood for over 60 years. It is not likely that the modern reinforced concrete panel houses built using the seamless method will last less long (by the way, the majority of such product's manufacturers believe that their 'fair' lifetime is at least 100 years). To sum up, we can say the following: the choice between construction methods today and in the near future is about personal preference and development location. That's why cast-in-place is most likely to be used in historic downtowns of unique structures, while panel houses will keep serving as the vast bulk for outskirts and suburb newbuilds. And the living standards both of cast-in-place and the panel houses will gradually become more equable.