Purpose:  The purpose is to investigate the use of concrete as a frame material and its effects on carbon dioxide emissions and energy use. Carbon dioxide emissions and energy use are examined from the production stage to the management stage 100 years in the future. In addition, investigate other material compositions in concrete to study the possibilities 0f lower carbon dioxide impact and energy use. Method: The methods used have included investigating one construction project involving two multi-family houses with the same conditions. The investigation conducted is primarily made through calculations of CO2 emission and energy use. Furthermore, a literary study has also been conducted focused on investigating what the impact concrete has on the environment and what different alternatives are available to reduce potential carbon dioxide emissions and energy use in house construction with a concrete frame. The study has focused on both the production phase and the management phase. The construction stage has been investigated primarily within the concrete production, enforcement and including transports. Whereas the management stage has been studied upon the energy use of the buildings and its effect on carbon dioxide emission.  The literature study deals with methods that can be associated with the case study but will also deal with other presumptive methods. Results: The study of the construction project shows that CO2 emission and energy use primarily comes from cement production within the production stage. Whereas, looking at the whole life cycle studied, the primary contributor to CO2 emissions and energy use over time is the management stage of the buildings. The result also shows that by using renewable steel as reinforcement can significantly effect the energy use, as well as, CO2 emission of the production phase. Conclusions: The cement production is one of the biggest causes of CO2 emissions and energy use in the production phase of the studied life cycle. While the management phase is the largest in terms of the total life cycle studied. Several methods are possible to decrease the use of energy use and CO2-emission in the production stage, and to combine those methods is an alternative that suggested

In order to maintain a sustainable construction industry, it is important to consider sustainability aspects in buildings. Material selection and optimizations are a fundamental part of this process. The purpose of this degree project is to contrast cross laminated timber slabs with prefabricated concrete slabs based on cost, carbon dioxide emissions, number of supports and the attitude of the construction industry. This is to see if one of the slabs can be considered more advantageous than the other and if it can be optimized. In order to achieve the aim and purpose of the study, a literature review, theoretical calculations and interviews with actors in the construction industry have been carried out. The study has resulted in a comparative analysis that shows that cross laminated timber slabs have a significantly lower carbon dioxide emission than prefabricated concrete slabs, but are less economically profitable. The result further shows that continuity can optimize both slabs through thinner thicknesses and thus be cost- and environmental-saving. The actors, in turn, have a tendency to prefer the materials that they are used to and feel safe working with, as there are risks involved in trying something newer. However, the actors show a great openness towards cross laminated timber and feel that its development will increase in connection with the knowledge about the material being established. The most central thing is to apply the right material in the right place. / För att upprätthålla en hållbar byggindustri är det viktigt att beakta hållbarhetsaspekter i byggnationer. Materialval och optimeringar är en grundläggande del av denna process. Syftet med det här examensarbetet är att ställa KL-träbjälklag mot prefabricerade betongbjälklag med utgångspunkt i kostnad, koldioxidutsläpp, antal upplag och byggbranschens inställning. Detta för att se om något av bjälklagen kan anses vara mer fördelaktigt än det andra och om det går att optimeras. För att uppnå studiens mål och syfte har en litteraturöversikt, teoretiska beräkningar och intervjuer med aktörer inom byggbranschen genomförts.  Studien har utmynnat i en jämförande analys som visar att KL-träbjälklag har ett betydligt mindre koldioxidutsläpp än prefabricerade betongbjälklag, men blir mindre ekonomiskt lönsamt. Resultatet visar ytterligare att kontinuitet kan optimera båda bjälklagen genom tunnare tjocklekar och på så vis vara kostnads- och miljöbesparande. Aktörerna i sin tur har en benägenhet att preferera de material som de är vana och trygga att arbeta med då det medför risker att bepröva något nyare. Aktörerna visar dock en stor öppenhet mot KL-trä och upplever att dess utveckling kommer att öka i samband med att kunskapen kring materialet etableras. Det mest centrala är att man tillämpar rätt material på rätt plats.

The choice of frame system is one of the first and most important steps in the design process. The decision is based on many key factors, including construction time, cost, and carbon footprint. There are studies that describe the different factors for various structural systems, but none that gather four of the most common systems in the same study. This study, conducted in collaboration with Skanska, analyzes a prefabricated CLT (Cross-Laminated Timber) structure, a prefabricated concrete structure, a hybrid structure combining CLT and concrete, and a combination structure with steel columns and a flat concrete base, in terms of time, cost, and CO2 footprint. Calculations and life cycle analyses have been performed on the four different frame systems, showing that the hybrid CLT and concrete structure performed the best overall in the three categories. The combination structure with steel columns and a flat concrete base followed, then the prefabricated concrete structure, and lastly the prefabricated CLT structure. Interviews with Skanska employees revealed that their knowledge and experience somewhat aligned with the results of the calculations and life cycle analyses, but the attitude towards continuing to work with the relatively new CLT structure was positive. / Valet av stomsystem är ett av de första och viktigaste stegen under projekteringsprocessen. Valet grundar sig på många viktiga faktorer, bland annat hur lång tid de tar att bygga, hur mycket det kostar och hur stort CO2-avtryck det har. Det finns studier som beskriver de olika faktorerna för olika stomsystem, men ingen som samlar fyra av de vanligaste stomsystemen i samma studie. Denna studie, i samarbete med Skanska, analyserar en prefabricerad KL-trästomme, en prefabricerad betongstomme, en hybridstomme i KL-trä och betong samt en kombinationsstomme med stålpelare och plattbärlag med avseende på just tid, kostnad och CO2-avtryck. Kalkyler och livscykelanalyser har gjorts på de fyra olika stomsystemen, vilket visar att hybridstommen i KL-trä och betong var den stomme som i sammantaget presterar bäst i de tre kategorierna. Kombinationsstommen med stålpelare och plattbärlag kom därefter, följ av den prefabricerade betongstommen och sist den prefabricerade KL-trästommen. Intervjuer med medarbetare på Skanska visade att den kunskap och erfarenhet som de besatt i viss mån stämde överens med de resultat som kalkyler och livscykelanalyser visade, men att inställningen till att fortsätta jobba med den relativt nya stommen i KL-trä är god.