Portlandsementti

Portlandsementtisäkkejä.

Portlandsementti on yleisin sementtityyppi. Sitä valmistetaan hienoksi jauhetusta Portlandklinkkeristä, johon on lisätty sitoutumisen säätöä varten kipsiä.[1]

Historia

Portlandsementin nimi tulee siitä, että se muistuttaa portlandkiveä, jota louhittiin Portlandin saarella Dorsetissa Englannissa. Vuonna 1824 englantilainen Joseph Aspdin patentoi portlandsementin valmistuksen.[2] Nykyisen tyyppisen portlandsementin valmistuksen voidaan katsoa alkaneen vasta vuonna 1843, kun niin ikään englantilainen Isaac Johnson paransi Aspdinin menetelmää polttamalla raaka-aineseoksen sintrauslämpötilaan asti. Kolmas portlandsementin valmistuksen yleistymiseen vaikuttanut englantilainen oli Frederick Ransome, joka vuonna 1885 patentoi raaka-aineseoksen polttamisen kiertouunissa. Tämä uusi valmistustekniikka paransi sementin laatua ja alensi merkittävästi kustannuksia. Menetelmä kehittyi nopeasti, ja 1900-luvun alussa kiertouuneja alettiin valmistaa teollisesti.

Portlandsementin valmistus Suomessa

Vuonna 1869 aloitettiin Saviolla sementin valmistus.[2] Vuosituotanto oli vain 4000 tonnia vuodessa, ja tehdas joutui lopettamaan 1894 huonon menekin vuoksi. Vanhimmat yhä toiminnassa olevat tehtaat ovat Finnsementin omistamat Paraisten sementtitehdas (1914) ja Lappeenrannan sementtitehdas (1938). Sementtiä on valmistettu myös Virkkalassa 1919–1994 ja Kolarissa 1968–1989.

Lähteet

  1. ↑ ”221 Sementti”, Rakennustekniikan käsikirja 2: Rakennusaineet ja -tarvikkeet. (Suomenkielisen laitoksen pohjana on ollut 1968 ilmestynyt uusittu laitos teoksesta BYGG, Hyvuddel 2. Materiallära) Helsinki: Tammi, 1970.
  2. ↑ a b Suomalainen sementti (PDF) (Sementin historia) Finnsementti Oy. Arkistoitu 2.12.2008. Viitattu 25.6.2009.

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