This answer assumes that you are not a citizen of any country whose nationals are allowed to travel to the UK without a visa. If you are a citizen of such a country, then you of course don't need a visa, but in that case you probably wouldn't have asked this question.
Your civil union document will not by itself exempt you from a visa. You can use it in combination with your residence card, however, if and only if your residence card says that it is the "residence card of a family member of an EU citizen" or words to that effect.
Because your card does say that, as shown in the image you've added, you can use it to travel to the UK without a visa. To do so, you should follow the procedures on the page about entering the UK as the holder of an article 10 residence card. Salient bits:
An Article 10 residence card should feature the wording “Residence Card of a Family Member of a Union Citizen”.
Another document, “Permanent Residence Card of a Family Member of a Union Citizen” issued under Article 20 of the Directive is also acceptable.
Documents issued on any other basis, for example (biometric) residence permits issued under the national law of another Member State are not acceptable and do not exempt the holder from the requirement to obtain an EEA family permit.
For example, a non-EEA spouse of a German national living in Germany will usually hold a residence permit issued under German domestic law. Therefore, a United Kingdom EEA family permit is required for travel and entry to the UK.
A valid, genuine Article 10 (or Article 20) residence card allows the non-EEA national family member of an EEA national to travel to the UK without the requirement to obtain an EEA family permit.
However, in order to be admitted to the UK you will need to demonstrate that you have a right of admission under EU law. Without evidence that you have a right of admission, you will not be allowed to enter to the UK on the basis of your residence card.
In order to be admitted to the UK, we would expect to see the following in addition to your valid residence card:
- your valid passport
- evidence that you are the family member of an EEA national (for example, your marriage certificate or birth certificate)